What is a computer virus

What is a Computer Virus? How Can You Protect Yourself?

A computer virus is one of the most dangerous kinds of malware. It spreads from device to device by replicating itself. Once it has infected a device, it can cause plenty of damage, including the deletion of files and programs and even the reformatting of your operating system.

Viruses spread through different means, such as email attachments, malicious files and removable storage devices. They are also of different kinds, primarily based on the part of the computer they infect. We cover 8 different kinds of viruses in the article below.

Given the threat posed by computer viruses, it’s important to know how to prevent them. Some important tips include:

The rest of the article provides more information on the different kinds of viruses and how to remove a virus if your device has been infected.

One of the most destructive forms of malware is the computer virus. Viruses can destroy your data, infect your files, and severely damage your computer. Computer viruses can also spread on their own and infect other computers. But are computer viruses still a concern?

The AV-Test Institute reports that there are more than 1.3 billion malware programs in existence as of 2022. Considering estimates find that 10% of all malware in 2022 are computer viruses, yes, they still pose a huge threat.

But what is a computer virus exactly? How do they get on your computer or device? In the article below, we’ll break down everything you need to know about computer viruses, what you can do to prevent infection and how to get rid of them.

What is a Computer Virus?

A computer virus is a type of malware with the ability to self-replicate. Think of a computer virus like the flu. The flu spreads from person to person, and once you get sick, your body is sluggish and can’t function like it normally would.

The same goes for a computer virus. They’re designed to wreak havoc, damage infected devices and cause them to function poorly. It’s essentially an application or computer code programmed to spread within and between devices. Once on a device, viruses can spread to other files and programs without the user’s consent.

Viruses can delete a few files, or completely take over your device and reformat system software.

How Do Viruses Infect Your Computer?

There are many different ways that computer viruses can infect your computer. But some are more prevalent than others. Here are some of the most common ways viruses find their way onto your device.

1. Spam emails and attachments

Security analysts have found anywhere from 75% to 94% of all malware is delivered by email. This can happen by opening an email attachment, or in some cases, by simply viewing the email. Some viruses are also delivered in the HTML body of the email. As a result, many email services disable HTML until you confirm you know the sender.

2. Instant messaging

Instant messaging services such as Skype and Facebook Messenger can also be used to spread viruses. The most common method is sending an infected link in a chat message. People are more likely to click on a link from someone they know, and virus developers are well aware of this.

3. File-sharing services

Dropbox, SharePoint, and other file-sharing services are other means of spreading viruses. If a user uploads an infected file to a file-sharing account, the computer virus will spread to anyone else with access to that account. Although Google Drive and some other services scan files for viruses, they only scan files smaller than 25MB.

4. Fake antivirus downloads

Sometimes, cybercriminals send pop-up ads to trick users into thinking their PC has a virus. They insist the user download their antivirus program to remove the threat. However, the antivirus download is a fake one, and it infects the user’s computer with a virus. This one adds insult to injury.

5. Unpatched software

The term unpatched software refers to software that isn’t up-to-date. Developers often release security updates to patch up vulnerabilities in the software, and it is essential to actually install these updates. Cybercriminals often take advantage of these vulnerabilities to infect computers with viruses and other malware.

6. Hardware

USB drives and other removable storage devices can contain viruses and spread them to your computer. While this isn’t quite as common, bad actors have been known to leave USB drives riddled with viruses for unsuspecting victims. If you’re not sure where it came from, it’s not a good idea to stick hardware into your computer.

8 Types of Computer Viruses

Some computer viruses begin replicating as soon as they get onto your device, while others require a trigger for the virus code to activate. Here’s an overview of the most common types of viruses and how they spread.

1. Boot sector virus

A computer virus that infects a computer’s master boot record and often spreads through removable storage devices and media. It is difficult to remove and usually requires the entire hard drive of infected computers to be reformatted.

2. Overwrite virus

A computer virus that infects your files and destroys them. The only way to remove it is to delete all the infected files, resulting in the loss of data contained in them. Overwrite viruses most commonly spread through emails.

3. Resident virus

This kind of computer virus embeds in the computer’s memory. If the original virus is deleted, a copy of it can remain in the infected computer’s memory. It can then be activated when your operating system performs certain functions. Since these viruses hide in your RAM, they often go undetected by antivirus software.

4. File-infecting virus

A computer virus that overwrites or inserts infected code into executable files. When the infected program is opened, the virus overwrites or destroys it. File-infecting viruses can also spread to a computer’s operating system or even reformat your hard drive.

5. Macro virus

A computer virus is written in the same macro language as software programs like Microsoft Office. They embed malicious code in these documents and data files, which begin to run when the files are opened. The virus may then infect all of the user’s documents, altering them or making them unreadable. The virus spreads if the user shares an infected document.

6. Web scripting virus

A virus that hides in the code of web pages and web browsers. Accessing web pages whose code contains such viruses can lead to your device being infected.

7. Polymorphic virus

Polymorphism refers to the ability to exist in multiple forms. Consequently, polymorphic viruses acquire a different form each time the infected file or program is executed by changing their code. This helps them avoid detection.

8. Multipartite virus

A multipartite virus can be thought of as a combination of the different types described above. It attacks using different vectors and infects different computer parts, such as the operating system, files and programs.

What Are Some Symptoms of a Computer Virus?

Certain warning signs indicate your computer might have a computer virus. These are some common signs that your computer may be infected.

If your device is exhibiting one or more of these symptoms, you’ll need to take action. We’ll show you how to do that below.

How to Get Rid of a Computer Virus

While malicious computer code spreads like the flu, there’s one major difference between the two. Unlike the flu, we have a cure for computer viruses.

In years past, new computer viruses could be extremely difficult to root out. While there has been an influx of malicious computer viruses and other malware (estimates say 350,000 new malware programs and apps are created every day), we’ve also had growth in the antivirus and cybersecurity industries to combat it.

There are several steps you should take if your computer has a virus. The steps will differ depending on whether you have a PC or a Mac.

Step-by-step guide: How to remove a virus from a Windows laptop or PC

If you think you have a virus, here’s what you’ll need to do to get rid of it.

1. Download a virus scanner

To catch and remove the latest virus threats, you’ll need a solid antivirus program. For rooting out viruses from a Windows device and effective real-time protection we can recommend Bitdefender. If you’re not looking for a paid service, check out our list of the best free antivirus programs.

You’ll want to have your scanner downloaded before the next step.

2. Disconnect from the internet

Since viruses can spread through the internet, you’ll want to disconnect from your Wi-Fi or ethernet. This way, you can focus solely on the infected device.

3. Enter Safe Mode

Turn your computer off. Now turn it on again, but keep pressing the F8 button as it boots up. An Advanced Boot Options menu will appear, and you should select the option Safe Mode with Networking.

4. Delete temporary files with your Disk Cleanup tool

Using this tool will allow you to delete all of your temporary files. To find it, begin by clicking on your Start menu, followed by Programs > Accessories > System Tools > Disk Cleanup.

Select Temporary Files from the File to Delete list, and go ahead and delete them. It’s possible you might catch the virus here, but you’ll definitely want to take the next step.

5. Run a virus scan

Begin by running your on-demand scanner, and then run your real-time scanner. Usually, there are quick scan and full system scan options. Go with a full system scan. Most likely, one of these programs will detect the virus and remove it. If the scans fail to remove the virus, then you need to remove it manually. Using Windows Registry, you can do this yourself, but it’s often safer to recruit an IT expert to assist you.

6. Check for updates

When you’ve removed the virus, make sure you install any software updates for Windows. Microsoft regularly releases updates to keep your device as secure as possible from the latest threats. Just click Windows Start menu > Settings > Update & Security. There you’ll see the latest updates for Windows.

7. Enable firewall

Firewalls also protect you from cyberattacks and viruses and should be enabled on your new antivirus. On Windows you can click Windows Start menu > Settings > Update & Security > Windows Security > Firewall and network protection to make sure it’s updated.

Step-by-step guide: How to remove a virus from a Mac

Though Macs aren’t as widely targeted as PCs, they’re definitely not invulnerable to attacks. Plus, Mac-specific malware might be even harder to get at than others. Here’s what you’ll need to do to get viruses off your Mac.

1. Download an antivirus scanner for Mac

For Macs, we recommend Avast Security. This scanner has improved significantly over the years. It offers premium virus malware detection with minimal impact on Mac system performance. They’ve got an excellent virus removal tool customized specifically for Mac. If you’ve got the time, check out our full guide on antivirus programs for Mac.

2. Disconnect from the internet

Remember that viruses can spread through the internet, so you’ll want to disconnect. Turn off your Wi-Fi router, or unplug your ethernet cable.

3. Run a virus scan

Your Mac-focused scanner should root out any viruses causing trouble. Especially Avast Security. If you want to find and remove any files on your Mac manually, try the next step.

4. Launch your Activity Monitor

If you want to find the compromised app or program manually, use your Activity Monitor. You should look for suspicious processes which aren’t linked to the programs you usually. When you find the malware, click on Quit Process and exit the Activity Monitor. To be doubly sure, you can Google the name of the suspicious process before quitting it in the Activity Monitor.

5. Move the malware into Trash

After closing the Activity Monitor, open your Applications folder. From there, move the malware into Trash and empty it.

6. Check for updates

Check if your software and apps are up to date. If there are any OS fixes or Apple Updates, install them immediately.

7. Enable firewall

Your new antivirus software will typically have a firewall installed, or you can toggle it in your program. But if you want to turn on the Mac firewall, go to System Preferences > Security & Privacy > Firewall.

How Can I Protect Myself From Computer Viruses?

The best defense against computer viruses is prevention. There are many different steps you can take to protect your computer and devices from a computer virus and other kinds of malware. Here are the essential tips:

Install antivirus software

Make sure you install antivirus software from a reputable company and keep it updated. While these scanners will keep your device as clean as a whistle, they also offer real-time protection. Good antivirus blocks suspicious connections, warns you of phishing sites, emails and messages, and catches potential injections before they happen.

A few leading antivirus programs we’ve reviewed include:

Keep your computer and software updated

Whether it’s macOS, Windows, iOS or Android, always install computer and software updates when they are available. These updates often fix security vulnerabilities in your operating system and software that help keep computer viruses at bay.

Don’t open suspicious emails or attachments

Delete or mark suspicious emails as spam and don’t open them. You should also select an email provider that scans all attachments before opening them.

Install anti-malware apps

In addition to antivirus software, consider using an anti-malware program app. These apps regularly scan your computer for viruses, spyware, and other malware. They also protect you from new, more harmful malware like the BloodyStealer. Just make sure that you’re only downloading legitimate apps from verified stores like Apple or Microsoft App store, or Google Play.

Install a firewall

A firewall screens internet and network traffic to help block potential threats. Strong firewalls will block viruses and other malware from getting to your device. Most strong antivirus programs have built-in firewalls that are enabled upon installation. Microsoft and Macs also have their own firewalls that have been improved over the years, you’ll just need to make sure they’re activated.

Adjust your browser and device privacy settings

Make sure to turn your browser’s privacy settings on and use a pop-up blocker. Many users flock to Chrome, but you can actually make Mozilla an anonymous browser if you tweak it right. You should also clear your cache and browsing history regularly. If you’re running Windows, check out our Windows 10 privacy guide and Windows 11 update. For Mac users, look at this privacy settings tutorial.

How Common are Computer Viruses?

Viruses are still a prevalent form of malware affecting household computers. While ransomware has taken center stage, it’s estimated that computer viruses comprise about 10% of all malware. But considering that the AV-Test Institute says 560,000 new pieces of malware are discovered every day (and about 1 billion malware programs are in existence) viruses still remain a huge threat.

Here are a few stats we’ve rounded up.

Are Malware and Computer Viruses the Same?

The terms malware and virus are often used interchangeably. However, they do not mean the same thing. Malware is a broad term for all kinds of malicious code or programs, regardless of how they function. A virus is a kind of malware that spreads by replicating itself across and within devices. It’s usually programmed to harm the infected device in some way.

The term malware can be used to refer to a virus, or other kinds of malware such as killware, worms and keyloggers. By 2022, ransomware and Ransomware-as-a-Service (RaaS) have become the most headline-stealing form of malware.

Final Thoughts

Cybercriminals have increasingly used viruses to target businesses, healthcare organizations, and governments in recent years. These viruses can breach data, damage the organizations’ operations, and destroy essential information.

Computer viruses remain a major cybersecurity threat to personal computer users. They can be extremely destructive and often destroy data or seriously damage computers. For these reasons, computer users need to be aware of this malware threat and protect their devices from viruses.

If you’re looking for quick answers to some of the more pressing questions regarding computer viruses and how to deal with them, check out the FAQ section below.

What causes virus on computer?

Viruses can infect computers in many different ways. The most common methods include malicious email attachments, removable storage devices, unpatched software and file-sharing services.

What happens if your computer gets a virus?

Viruses can severely impact the performance of your computer or device. Some notable effects of a computer virus infection include:

For more information on the impacts of computer viruses, read this comprehensive article on computer viruses.

How do you take viruses off your computer?

The surest way to remove a virus from your device is by installing a reliable antivirus program and running constant updates. You should also regularly update the antivirus software to ensure you have the latest library of viruses.

Manually removing viruses is a more complicated process. Check out this computer virus article for more information on how you can do this on both Windows and Mac devices.

How do I prevent computer viruses?

Preventing computer viruses is far easier than removing them once you’ve been infected. The following steps should help prevent a computer virus infection:

Malware & Computer Virus Facts & FAQs

Whether you’re on a Windows, Apple or Linux computer, a desktop, laptop, smartphone or tablet, you’re vulnerable to ever-evolving cyberthreats from computer viruses and other types of malware. The first step to protecting yourself and your data is understanding what you’re up against. Here’s an overview of the major types of malware, today’s most common computer viruses and their potential impact.

The term «malware» — an amalgamation of malicious and software — is now used to describe any malicious computer program on a computer or mobile device. These programs are installed without the consent of users and can cause a number of unpleasant effects, including crippling computer performance, mining your system for personally identifiable information (PII) and sensitive data, erasing or encrypting data or even hijacking device operations or computer-controlled hardware. Hackers continuously develop increasingly sophisticated ways to infiltrate user systems. Like a game of whack-a-mole, as soon as one threat is neutralized, a replacement evolves, and the next iteration emerges. Let’s look at some of the most common types of malware currently in use.

1. Computer Viruses

What is a computer virus? Computer viruses are a type of malware that earned their name because of how they spread by «infecting» other files on a disk or computer. Viruses then spread to other disk drives and machines when the infected files are received in downloads from websites, email attachments, shared drives or when carried in files on physical media, such as USB drives or—in the early days—floppy disks.

According to the National Institute of Standards and Technology (NIST), the first computer virus, a boot sector virus called «Brain,» was developed in 1986. Tired of customers pirating software from their shop, two brothers claim to have designed the virus to infect the boot sector of software thieves’ floppy disks. The virus spread through infected copies of the pirated software, jumping from the infected floppy disk to the computer hard drive when the program was booted, or loaded onto the new machine.

2. Worms

Unlike viruses, worms don’t require human help in order to infect, self-replicate or propagate. As soon as they breach a system, they infect their entry point and spread through the device and across any network to which the device connects. By exploiting network vulnerabilities—such as missed operating system (OS) updates or application patches, weak email security or poor internet safety practices—worms can execute, self-replicate and propagate at an almost exponential rate as each new infection repeats the process. Originally, most worms simply «ate» system resources and reduced performance. Now, most worms contain malicious «payloads» designed to steal or delete files upon execution.

3. Adware

One of the most common online nuisances is adware. Adware programs automatically deliver advertisements to host computers. Familiar examples of adware include pop-up ads on webpages and advertising messages that are part of the interface of «free» software. While some adware is relatively harmless, other variants use tracking tools to glean information about your location or browser history. Most of the time, adware collects information in order to serve better targeted ads. But sometimes Adware is used for more nefarious purposes including redirecting search results, displaying op-ups that can’t be closed or link to malware, disabling antivirus software or even going all the way off the rails into the territory of spyware—see #4.

Technically, adware is installed with people’s knowledge and consent. But when was the last time you read all the way through a several thousand word «Terms of Service» statement? By clicking the «I Agree» button, you grant consent. Because you have acknowledged and consented to the terms of service, these programs can’t be termed malware. Today’s antivirus software typically identifies these programs as «potentially unwanted programs» (PUPs).

4. Spyware

Spyware does just what it says. It spies on what you’re doing at your computer. It collects data such as keystrokes, browsing habits, location data and even login information. While adware might include «repurposing» collected data for sale in the terms of service statement, spyware is more duplicitous. Spyware is considered malware because users are unaware of it. The only intent of spyware is malicious. Spyware collects and sells your data to third parties, typically cyber criminals, with no regard for how the data will be used. Spyware may also modify specific security settings on your computer or interfere with network connections.

In another example of how the line between adware and spyware can blur, the rise of mobile computing has seen an explosion of spyware that tracks user behavior across devices and physical locations without their consent. For example, a free weather app on your smartphone may have gotten your consent to collect and use your location data, ostensibly to provide more accurate forecasts. You agreed to the app’s terms of service which include language enabling to re-use the location as they see fit, so it’s legit. But what happens when that includes selling your location to data to anyone who can afford it, regardless of whether that an online store trying to populate banner ads in your browser or a cyber criminal who cross-references mobile phone user data with other data sources?

5. Ransomware

Ransomware infects your computer, encrypts your PII and other sensitive data such as personal or work documents and then demands a ransom for their release. If you refuse to pay, the data is deleted. Some ransomware variants lock out all access to your computer. Sometimes, they might claim to be the work of legitimate law enforcement agencies and suggest that you’ve been caught doing something illegal.

6. Bots

Bots are programs designed to automatically carry out specific operations. Although they serve many legitimate purposes, they are also a popular type of malware. Once on a computer, bots can cause the machine to execute specific commands without the user’s approval or knowledge. Hackers may also try to infect multiple computers with the same bot to create a «botnet»—short for robot network. These zombie botnets give hackers the ability to remotely manage compromised computers, enabling them to steal sensitive data, to spy on user activities, to distribute spam automatically or to launch devastating Distributed-Denial-of-Service (DDoS) attacks on computer networks and websites.

7. Rootkits

Rootkits allow remote access or control of a computer by a third party. These programs are useful for IT professionals trying to troubleshoot network issues remotely, but they can easily become nefarious. Once installed on your computer, rootkits allow attackers to take complete control of your machine to steal data or install additional malware. Rootkits are designed to go unnoticed and actively hide their presence and that of other malware that they install.

As with most computer viruses and malware, although it’s no guarantee of safety, protecting your devices from rootkits starts with keeping current on all OS and application updates and patches to eliminate potential infection routes. Effective detection of rootkits requires real-time monitoring—not just periodic disk drive scans—for unusual behavior system behavior.

8. Trojan Horses

Commonly called «Trojans,» these programs hide in plain sight by masquerading as legitimate files or software. Once downloaded and installed, Trojans make changes to a computer and carry out malicious activities, without the knowledge or consent of the victim.

9. Bugs

Bugs—flaws in software code—are not a type of malware, they are errors in software code that popular vectors for attackers with malicious intent. Bugs can, on and of themselves, have detrimental effects on your computer, such as freezing, crashing or reducing performance. Security bugs create holes in a computer or network’s defenses that are especially attractive to would-be attackers. While better security control on the developer end helps reduce the number of bugs, bugs are another reason why keeping current on software patches and system updates is crucial.

Common Computer Virus Myths

Common Misconceptions About Malware

Malware threats often rely on common misconceptions to create soft targets. By understanding some of the most widely misunderstood points, simple shifts in behavior can remove you from the soft target list.

One of the most common misconceptions about malware is the assumption that infection is obvious. Users often assume they’ll know if their computer has been compromised. Typically, however, the intent of malware is to perform their task(s) for as long as possible. So, malware doesn’t leave a trail to follow, and your system displays no signs of infection. Even malware like ransomware only makes its presence known after it has encrypted the files, thus completing its first task, to be ransomed back to the user.

Another common misconception is that all reputable websites are safe. Compromising legitimate websites with infected code is one of the easiest ways to convince potential victims to download files or provide sensitive information. This is exactly what happened to the European Central Bank (ECB) in August of 2019.

Many users believe their personal data—photos, documents and files—have no value for malware creators. But cyber criminals mine publicly available data, like that on social networks, to create custom targeted attacks on individuals or to gather intelligence for spear phishing emails popular for accessing the networks and assets of large, otherwise secure organizations.

Methods of Malware and Virus Infection and Spread

So how does your computer become infected by computer viruses or malware? There are many common approaches, but the following are some of the most popular methods owing to their efficacy and simplicity:

Confidential data, such as passwords, are a key target of cyber criminals. In addition to using malware to capture passwords, cyber criminals also collect login details from hacked websites and devices, even physical means like peering over your shoulder in a crowded cafe. That’s why it’s so important to use a unique and complex password for each online account. This means 15 character or more and including letters, numbers and special characters.

The easiest way to do this is through a password manager tool that generates random passwords, stores them securely and obtains validation/permission prior to entering the stored credentials while masking the characters. Because so many people re-use passwords, password tools ensure that one compromised account does not cascade through your entire digital ecosystem. Also, remember that many security verification questions are ineffective. For example, if the question is «What’s your favorite food?» and you’re in the United States, «Pizza» is a common answer.

Signs of Malware and Computer Virus Infections

While most malware leaves no telltale signs and leaves your computer operating normally, sometimes there can be indications that you might be infected. Reduced performance tops the list. This includes slow-running processes, windows that take longer to load than usual and seemingly random programs running in the background. You may also notice that internet homepages have been changed in your browser, or that pop-up ads are occurring more frequently than usual. In some cases, malware can also impact more basic computer functions: Windows may not open at all, and you may be unable to connect to the internet or access higher-level system control functions.

If you suspect that your computer might be infected, scan your system immediately. If nothing is found, but you’re still in doubt, get a second opinion by running an alternative antivirus scanner. Check out these free tools: Free Cloud Anti-Virus Software and Free Ransomware Protection & Decryption Tools

Ideally, you want to prevent an attack, not discover it. While you should scan your device as soon as you suspect something amiss, your best defense is a comprehensive internet security solution that includes real-time scanning and monitoring of disk drives, files and activities as well as real-time updates on web threats provided by a team of experienced cyber security professionals. This includes monitoring instant messaging services, scanning email attachments, providing a firewall and so much more than scheduled scans and periodic updates. Effective antivirus and cyber security software should be able to work and coordinate between all your devices—how else can they protect you from viruses and malware that do the same?

Other helpful reads and links related to Computer Viruses and Malware

Malware & Computer Virus Facts & FAQs

Computer viruses & other types of malware are a constant & evolving threat to all computer & mobile device users. Learn about today’s malware to stay safe.

What Is a Computer Virus?

Definition

A computer virus is a malicious application or authored code used to perform destructive activity on a device or local network. The code’s malicious activity could damage the local file system, steal data, interrupt services, download additional malware, or any other actions coded into the program by the malware author. Many viruses pretend to be legitimate programs to trick users into executing them on their device, delivering the computer virus payload.

Types of Computer Viruses

Every virus has a payload that performs an action. The threat actor can code any malicious activity into the virus payload, including simple, innocuous pranks that don’t do any harm. While a few viruses have harmless payloads, most of them cause damage to the system and its data. There are nine main virus types, some of which could be packaged with other malware to increase the chance of infection and damage. The nine major categories for viruses are:

Boot Sector Virus

Your computer drive has a sector solely responsible for pointing to the operating system so that it can boot into the interface. A boot sector virus damages or controls the boot sector on the drive, rendering the machine unusable. Attackers will usually spread this virus type using a malicious USB device. The virus is activated when users plug in the USB device and boot their machine.

Web Scripting Virus

Most browsers have defenses against malicious web scripts, but older, unsupported browsers have vulnerabilities that allow an attacker to run code on the local device.

Browser Hijacker

A virus that can change the settings on your browser will hijack browser favorites, the home page URL, your search preferences and redirect you to a malicious site. The site could be a phishing site or an adware page used to steal data or make money for the attacker.

Resident Virus

A virus that can access computer memory and sit dormant until a payload is delivered is considered a resident virus. This malware may stay dormant until a specific date, time, or a user performs an action.

Direct Action Virus

When a user executes a seemingly harmless file attached with malicious code, direct action viruses deliver a payload immediately. These viruses can also remain dormant until a specific action is taken or a timeframe passes.

Polymorphic Virus

Malware authors can use polymorphic code to change the program’s footprint to avoid detection. Polymorphic viruses make it more difficult for an antivirus to detect and remove them.

File Infector Virus

To persist on a system, a threat actor uses file infector viruses to inject malicious code into critical files that run the operating system or important programs. When the system boots or the program runs, the virus is activated.

Multipartite Virus

These malicious programs spread across a network or other systems by copying themselves or injecting code into critical computer resources.

Macro Virus

Microsoft Office files can run macros, and these macros can be used to download additional malware or run malicious code. Macro viruses deliver a payload when the file is opened, and the macro runs.

What Causes Computer Viruses?

Computer viruses are standard programs; only instead of offering useful resources, these programs can damage your device. For a threat actor to execute a virus on your machine, you must initiate execution. In some cases, an attacker can execute malicious code through your browser or remotely from another network computer. Modern browsers have defenses against local machine code execution, but third-party software installed on the browser could have vulnerabilities that allow viruses to run locally.

The delivery of a computer virus can happen in several ways. One common method is via a phishing email. Another technique is hosting malware on a server that promises to provide a legitimate program. It can be delivered using macros or by injecting malicious code into legitimate software files.

What Is a Computer Worm?

A computer worm is malware, just like a virus, but a worm takes a copy of itself and propagates it to other users. Worms can also deliver a payload and exhaust resources. For example, an email worm sends a copy of itself to everyone on an infected user’s email contact list. When it reaches recipient inboxes, anyone who runs the worm sends it to their contact list. Email worms exhaust storage space and spread very quickly across the internet, so they create issues differently than a virus.

What Does a Computer Virus Do?

The way a computer virus acts depends on how it’s coded. It could be something as simple as a prank that doesn’t cause any damage, or it could be sophisticated, leading to criminal activity and fraud. Many viruses only affect a local device, but others spread across a network environment to find other vulnerable hosts.

A virus that infects a host device will continue delivering a payload until it’s removed. Most antivirus vendors have small removal programs that eliminate the virus. Polymorphic viruses make it difficult for removal because they change their footprint consistently. The payload could be stealing data, destroying data, or interrupting services on the network or the local device.

Symptoms of Computer Virus

Malware authors write code that is undetectable until the payload is delivered. However, like any software program, bugs could present issues while the virus runs. Signs that you have a computer virus include:

Examples of Computer Virus

The web contains millions of computer viruses, but only a few have gained popularity and infect record numbers of machines. Some examples of widespread computer viruses include:

How to Prevent Computer Viruses

Computer viruses can damage your PC, send sensitive data to attackers, and cause downtime until the system is repaired. You can avoid becoming the next computer virus victim by following a few best practices:

What Are Computer Viruses?

Definition of Computer Viruses

A computer virus is a type of malicious software, or malware, that spreads between computers and causes damage to data and software.

Computer viruses aim to disrupt systems, cause major operational issues, and result in data loss and leakage. A key thing to know about computer viruses is that they are designed to spread across programs and systems. Computer viruses typically attach to an executable host file, which results in their viral codes executing when a file is opened. The code then spreads from the document or software it is attached to via networks, drives, file-sharing programs, or infected email attachments.

Common Signs of Computer Viruses

A computer virus will more than likely have an adverse effect on the device it resides on and may be discoverable through common signs of performance loss, including:

Speed of System

A computer system running slower than usual is one of the most common signs that the device has a virus. This includes the system itself running slowly, as well as applications and internet speed suffering. If a computer does not have powerful applications or programs installed and is running slowly, then it may be a sign it is infected with a virus.

Pop-up Windows

Unwanted pop-up windows appearing on a computer or in a web browser are a telltale sign of a computer virus. Unwanted pop-ups are a sign of malware, viruses, or spyware affecting a device.

Programs Self-executing

If computer programs unexpectedly close by themselves, then it is highly likely that the software has been infected with some form of virus or malware. Another indicator of a virus is when applications fail to load when selected from the Start menu or their desktop icon.

Accounts Being Logged Out

Some viruses are designed to affect specific applications, which will either cause them to crash or force the user to automatically log out of the service.

Crashing of the Device

System crashes and the computer itself unexpectedly closing down are common indicators of a virus. Computer viruses cause computers to act in a variety of strange ways, which may include opening files by themselves, displaying unusual error messages, or clicking keys at random.

Mass Emails Being Sent from Your Email Account

Computer viruses are commonly spread via email. Hackers can use other people’s email accounts to spread malware and carry out wider cyberattacks. Therefore, if an email account has sent emails in the outbox that a user did not send, then this could be a sign of a computer virus.

Changes to Your Homepage

Any unexpected changes to a computer—such as your system’s homepage being amended or any browser settings being updated—are signs that a computer virus may be present on the device.

How Do Computer Viruses Attack and Spread?

In the early days of computers, viruses were spread between devices using floppy disks. Nowadays, viruses can still be spread via hard disks and Universal Serial Bus (USB) devices, but they are more likely to be passed between devices through the internet.

Computer viruses can be spread via email, with some even capable of hijacking email software to spread themselves. Others may attach to legitimate software, within software packs, or infect code, and other viruses can be downloaded from compromised application stores and infected code repositories. A key feature of any computer virus is it requires a victim to execute its code or payload, which means the host application should be running.

Types of Computer Viruses

There are several types of computer viruses that can infect devices. This section will cover computer virus protections and how to get rid of computer viruses.

Resident Virus

Viruses propagate themselves by infecting applications on a host computer. A resident virus achieves this by infecting applications as they are opened by a user. A non-resident virus is capable of infecting executable files when programs are not running.

Multipartite Virus

A multipartite virus uses multiple methods to infect and spread across computers. It will typically remain in the computer’s memory to infect the hard disk, then spread through and infect more drives by altering the content of applications. This results in performance lag and application memory running low.

Multipartite viruses can be avoided by not opening attachments from untrusted sources and by installing trusted antivirus software. It can also be prevented by cleaning the boot sector and the computer’s entire disk.

Direct Action

A direct action virus accesses a computer’s main memory and infects all programs, files, and folders located in the autoexec.bat path, before deleting itself. This virus typically alters the performance of a system but is capable of destroying all data on the computer’s hard disk and any USB device attached to it. Direct action viruses can be avoided through the use of antivirus scanners. They are easy to detect, as is restoring infected files.

Browser Hijacker

A browser hijacker manually changes the settings of web browsers, such as replacing the homepage, editing the new tab page, and changing the default search engine. Technically, it is not a virus because it cannot infect files but can be hugely damaging to computer users, who often will not be able to restore their homepage or search engine. It can also contain adware that causes unwanted pop-ups and advertisements.

Browser hijackers typically attach to free software and malicious applications from unverified websites or app stores, so only use trusted software and reliable antivirus software.

Overwrite Virus

Overwrite viruses are extremely dangerous. They can delete data and replace it with their own file content or code. Once files get infected, they cannot be replaced, and the virus can affect Windows, DOS, Linux, and Apple systems. The only way this virus can be removed is by deleting all of the files it has infected, which could be devastating. The best way to protect against the overwrite virus is to use a trusted antivirus solution and keep it updated.

Web Scripting Virus

A web scripting virus attacks web browser security, enabling a hacker to inject web-pages with malicious code, or client-side scripting. This allows cyber criminals to attack major websites, such as social networking sites, email providers, and any site that enables user input or reviews. Attackers can use the virus to send spam, commit fraudulent activity, and damage server files.

Protecting against web scripting is reliant on deploying real-time web browser protection software, using cookie security, disabling scripts, and using malicious software removal tools.

File Infector

Network Virus

Network viruses are extremely dangerous because they can completely cripple entire computer networks. They are often difficult to discover, as the virus could be hidden within any computer on an infected network. These viruses can easily replicate and spread by using the internet to transfer to devices connected to the network. Trusted, robust antivirus solutions and advanced firewalls are crucial to protecting against network viruses.

Boot Sector Virus

A boot sector virus targets a computer’s master boot record (MBR). The virus injects its code into a hard disk’s partition table, then moves into the main memory when a computer restarts. The presence of the virus is signified by boot-up problems, poor system performance, and the hard disk becoming unable to locate. Most modern computers come with boot sector safeguards that restrict the potential of this type of virus.

Steps to protecting against a boot sector virus include ensuring disks are write-protected and not starting up a computer with untrusted external drives connected.

Know More About Computer Viruses Through Examples

There are common examples of what computer and internet users believe to be viruses, but are technically incorrect.

Is Trojan a Virus?

A Trojan horse is a type of program that pretends to be something it is not to get onto a device and infect it with malware. Therefore, a Trojan horse virus is a virus disguised to look like something it is not. For example, viruses can be hidden within unofficial games, applications, file-sharing sites, and bootlegged movies.

Is a Worm a Virus?

A computer worm is not a virus. Worms do not need a host system and can spread between systems and networks without user action, whereas a virus requires users to execute its code.

Is Ransomware a Virus?

Ransomware is when attackers lock victims out of their system or files and demand a ransom to unlock access. Viruses can be used to carry out ransomware attacks.

Is Rootkit a Virus?

A rootkit is not a virus. Rootkits are software packages that give attackers access to systems. They cannot self-replicate or spread across systems.

Is a Software Bug a Virus?

«Bug» is a common word used to describe problems with computers, but a software bug is not a virus. A bug is a flaw or mistake in software code, which hackers can exploit to launch a cyberattack or spread malware.

How To Prevent Your Computer From Viruses

There are several ways to protect your computer from viruses, including:

Use a Trusted Antivirus Product

Trusted computer antivirus products are crucial to stop malware attacks and prevent computers from being infected with viruses. These antivirus concepts will protect devices from being infected through regular scans and identifying and blocking malware.

Avoid Clicking Pop-up Advertisements

Unwanted pop-up advertisements are more than likely to be linked to computer viruses and malware. Never click on pop-up advertisements because this can lead to inadvertently downloading viruses onto a computer.

Scan Your Email Attachments

A popular way to protect your device from computer viruses is to avoid suspicious email attachments, which are commonly used to spread malware. Computer antivirus solutions can be used to scan email attachments for potential viruses.

Scan the Files That You Download Using File-sharing Programs

File-sharing programs, particularly unofficial sites, are also popular resources for attackers to spread computer viruses. Avoid downloading applications, games, or software from unofficial sites, and always scan files that have been downloaded from any file-sharing program.

How Fortinet Can Help

The Fortinet antivirus solution protects organizations from the latest strands of virus, spyware, and other security threats. Its advanced detection engines help users avoid downloading the latest and evolving threats, and prevents viruses from gaining a foothold inside organizations’ networks. The antivirus solution also reduces the threat of data breaches, protects against evolving malware variants, and keeps businesses up to date with regular updates.

What is a Computer Virus and its Types

Computer Virus

A computer virus is a malicious program that self-replicates by copying itself to another program. In other words, the computer virus spreads by itself into other executable code or documents. The purpose of creating a computer virus is to infect vulnerable systems, gain admin control and steal user sensitive data. Hackers design computer viruses with malicious intent and prey on online users by tricking them.

One of the ideal methods by which viruses spread is through emails – opening the attachment in the email, visiting an infected website, clicking on an executable file, or viewing an infected advertisement can cause the virus to spread to your system. Besides that, infections also spread while connecting with already infected removable storage devices, such as USB drives.

It is quite easy and simple for the viruses to sneak into a computer by dodging the defense systems. A successful breach can cause serious issues for the user such as infecting other resources or system software, modifying or deleting key functions or applications and copy/delete or encrypt data.

How does a computer virus operate?

A computer virus operates in two ways. The first kind, as soon as it lands on a new computer, begins to replicate. The second type plays dead until the trigger kick starts the malicious code. In other words, the infected program needs to run to be executed. Therefore, it is highly significant to stay shielded by installing a robust antivirus program.

Of late, the sophisticated computer virus comes with evasion capabilities that help in bypassing antivirus software and other advanced levels of defenses. The primary purpose can involve stealing passwords or data, logging keystrokes, corrupting files, and even taking control of the machine.

Subsequently, the polymorphic malware development in recent times enables the viruses to change its code as it spreads dynamically. This has made the virus detection and identification very challenging.

The History of Computer Virus

Robert Thomas, an engineer at BBN Technologies developed the first known computer virus in the year 1971. The first virus was christened as the “Creeper” virus, and the experimental program carried out by Thomas infected mainframes on ARPANET. The teletype message displayed on the screens read, “I’m the creeper: Catch me if you can.”

But the original wild computer virus, probably the first one to be tracked down in the history of computer viruses was “Elk Cloner.” The Elk Cloner infected Apple II operating systems through floppy disks. The message displayed on infected Apple Computers was a humorous one. The virus was developed by Richard Skrenta, a teenager in the year 1982. Even though the computer viruses were designed as a prank, it also enlightened how a malicious program could be installed in a computer’s memory and stop users from removing the program.

It was Fred Cohen, who coined the term “computer virus” and it was after a year in 1983. The term came into being when he attempted to write an academic paper titled “Computer Viruses – Theory and Experiments” detailing about the malicious programs in his work.

Types of Computer Viruses

A computer virus is one type of malware that inserts its virus code to multiply itself by altering the programs and applications. The computer gets infected through the replication of malicious code. Computer viruses come in different forms to infect the system in different ways. Find some of the most common type of computer viruses here,

Boot Sector Virus – This type of virus infects the master boot record and it is challenging and a complex task to remove this virus and often requires the system to be formatted. Mostly it spreads through removable media.

Direct Action Virus – This is also called non-resident virus, it gets installed or stays hidden in the computer memory. It stays attached to the specific type of files that it infect. It does not affect the user experience and system’s performance.

Resident Virus – Unlike direct action viruses, resident viruses get installed on the computer. It is difficult to identify the virus and it is even difficult to remove a resident virus.

Multipartite Virus – This type of virus spreads through multiple ways. It infects both the boot sector and executable files at the same time.

Polymorphic Virus – These type of viruses are difficult to identify with a traditional anti-virus program. This is because the polymorphic viruses alters its signature pattern whenever it replicates.

Overwrite Virus – This type of virus deletes all the files that it infects. The only possible mechanism to remove is to delete the infected files and the end-user has to lose all the contents in it. Identifying the overwrite virus is difficult as it spreads through emails.

Spacefiller Virus – This is also called “Cavity Viruses”. This is called so as they fill up the empty spaces between the code and hence does not cause any damage to the file.

Besides these, the other file infector viruses come as a completely included program or script sent in email attachments.

#Macro viruses:
As the name suggests, the macro viruses particularly target macro language commands in applications like Microsoft Word. The same is implied on other programs too.

In MS Word, the macros are keystrokes that are embedded in the documents or saved sequences for commands. The macro viruses are designed to add their malicious code to the genuine macro sequences in a Word file. However, as the years went by, Microsoft Word witnessed disabling of macros by default in more recent versions. Thus, the cybercriminals started to use social engineering schemes to target users. In the process, they trick the user and enable macros to launch the virus.

Since macro viruses are making a come back in the recent years, Microsoft quickly retaliated by adding a new feature in Office 2016. The feature enables security managers to selectively enable macro use. As a matter of fact, it can be enabled for trusted workflows and blocked if required across the organization.

#Overwrite Viruses:

The virus design purpose tends to vary and Overwrite Viruses are predominantly designed to destroy a file or application’s data. As the name says it all, the virus after attacking the computer starts overwriting files with its own code. Not to be taken lightly, these viruses are more capable of targeting specific files or applications or systematically overwrite all files on an infected device.

On the flipside, the overwrite virus is capable of installing a new code in the files or applications which programs them to spread the virus to additional files, applications, and systems.

#Polymorphic Viruses:
More and more cybercriminals are depending on the polymorphic virus. It is a malware type which has the ability to change or mutate its underlying code without changing its basic functions or features. This helps the virus on a computer or network to evade detection from many antimalware and threat detection products.

Since virus removal programs depend on identifying signatures of malware, these viruses are carefully designed to escape detection and identification. When a security software detects a polymorphic virus, the virus modifies itself thereby, it is no longer detectable using the previous signature.

#Resident Viruses:
The Resident virus implants itself in the memory of a computer. Basically, the original virus program is not required to infect new files or applications. Even when the original virus is deleted, the version stored in memory can be activated. This happens when the computer OS loads certain applications or functions. The resident viruses are troublesome due to the reason they can run unnoticed by antivirus and antimalware software by hiding in the system’s RAM.

#Rootkit Viruses:
The rootkit virus is a malware type which secretly installs an illegal rootkit on an infected system. This opens the door for attackers and gives them full control of the system. The attacker will be able to fundamentally modify or disable functions and programs. Like other sophisticated viruses, the rootkit virus is also created to bypass antivirus software. The latest versions of major antivirus and antimalware programs include rootkit scanning.

#System or Boot-record Infectors:

The Boot-record Infectors infect executable code found in specific system areas on a disk. As the name implies, they attach to the USB thumb drives and DOS boot sector on diskettes or the Master Boot Record on hard disks. Boot viruses are no more common these days as the latest devices rely less on physical storage media.

How To Avoid Email Viruses And Worms

Here are some simple rules you can follow to avoid being infected by viruses through email.

How To Be Safe From Email Viruses And Worms

Here are some simple rules you can follow to avoid being infected by viruses through email.

Do’s
1. Use a professional, email service such as Runbox. Subscription services provide higher levels of security and support.
2. Make sure that your Runbox virus filter is activated.
3. Use the Webmail interface at www.runbox.com to read your email, or don’t download all your email to an email client unseen. Screen your email first, and delete suspicious-looking and unwanted messages before downloading the legitimate email to your local email client.
4. Make sure your computer has updated anti-virus software running locally. Automatic updates are essential for effective virus protection. Combined with server-side scanning, you now have two layers of security.
5. Disable message preview in your email client, especially on Windows platforms. Otherwise, malicious programs attached to incoming messages may execute automatically and infect your computer.
6. Ignore or delete messages with attachments appearing to be sent from official Runbox email addresses. Runbox rarely sends email to our users, aside from replies to inquiries and payment reminders. We practically never send an email with attachments to users.
7. Take caution when opening graphics and media attachments, as viruses can be disguised as such files.
8. Maintain several independent email accounts. If a virus infects your only business email address, you’ll be in trouble. Also, keep backups of your most important email and files separately.
9. If any valid message headers of a virus-email indicate what server the message was sent from, contact the service in question and file a formal complaint.

Don’ts
1. Do not open an email attachment unless you were expecting it and know whom it’s from.
2. Do not open any unsolicited executable files, documents, spreadsheets, etc.
3. Avoid downloading executable or documents from the internet, as these are often used to spread viruses.
4. Never open files with a double file extension, e.g. filename.txt.vbs. This is a typical sign of a virus program.
5. Do not send or forward any files that you haven’t virus-checked first.
6. Viruses and spam
7. Virus-makers and spammers often cooperate in devious schemes to send as much spam as possible as efficiently as possible. They create viruses that infect vulnerable computers around the world and turn them into spam-generating “robots”. The infected computers then send massive amounts of spam, unbeknownst to the computer owner.

Such virus-generated email is often forged to appear to be sent from legitimate addresses collected from address books on infected computers. The viruses also use such data, combined with lists of common (user) names, to send spam to huge numbers of recipients. Many of those messages will be returned as undeliverable, and arrive in innocent and unknowing email users’ Inboxes. If this happens to you, use the trainable spam filter to catch those messages.

How To Get Rid Of Computer Virus

Never the neglect to take action on a computer virus residing in your system. There are chances that you might end up losing important files, programs, and folders. In some cases, the virus damages the system hardware too. Thereby, it becomes mandatory to have an effective anti-virus software installed on your computer to steer clear of all such threats.

Signs of Virus Infection

It is vital for any computer user to be aware of these warning signs –

• Slower system performance
• Pop-ups bombarding the screen
• Programs running on their own
• Files multiplying/duplicating on their own
• New files or programs in the computer
• Files, folders or programs getting deleted or corrupted
• The sound of a hard drive

If you come across any of these above-mentioned signs then there are chances that your computer is infected by a virus or malware. Not to delay, immediately stop all the commands and download an antivirus software. If you are unsure what to do, get the assistance of an authorized computer personnel. If you are confident enough, start investigating on your own by following the below mentioned step-by-step procedures.

#Safe Mode
Boot the system and press F8 for Advanced Boot Options menu. Select Safe Mode with Networking and press Enter. You might need to keep repeatedly pressing to get on to the screen.

Working on the Safe Mode helps handle nefarious files as they’re not actually running or active. Last but not the least the internet spreads the infection, so remove the connection.

#Delete Temporary Files
In order to free the disk space, delete temporary files before starting to run the virus scan. This approach helps speed up the virus scanning process. The Disk Cleanup tool helps in deleting your temporary files on the computer.

Here is how you got to go about accomplishing it – Start menu then select All Programs, now you click on Accessories, System Tools, and then click Disk Cleanup.

#Download Virus/Malware Scanner
If you are under the impression that a virus scanner cleanups the bad stuff from your computer then sadly, that’s not true! It helps in eliminating standard infections and not sufficient to remove the latest harmful infections. The virus/malware scanner helps to narrow down on the issue, so, download it now. In order to better protect go for a real-time anti-virus program, since it automatically keeps checking in the background for viruses.

P.S: Don’t install more than one real-time anti-virus program. If you do so, your system will start to behave weirdly.

#Run a Virus/Malware Scan
Download the virus/malware scanner using the internet. Once you have finished downloading the virus scanner, disconnect it for security and safety reasons. After successful download complete the installation procedures of the Virus/Malware scanner, then start running your on-demand scanner first and thereafter run your real-time scanner.

The reason for running both is that one of them will effectively eliminate your computer virus or malware.

#Reinstall the Software or Damaged Files
Once the virus removal from your computer is complete, go ahead and reinstall the files and programs that were damaged by the virus or malware. Make use of the backups for re-installation.

In simple, do the backups regularly and stay protected.

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