Infected computer with a computer virus icon next to a question mark and warning symbol
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Computer Viruses: A Quick Guide

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:

  1. Install antivirus software. We recommend Bitdefender.
  2. Keep your system software updated.
  3. Don’t open suspicious emails or attachments.
  4. Install anti-malware apps.
  5. Install or enable a firewall.
  6. Turn on your browser’s privacy settings.

Visit Bitdefender

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 reported that there were more than 1.3 billion malware programs in existence as of 2022. Considering estimates find that 10% of all malware in 2022 were 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?

Computer virus iconA 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.

6 ways in which a computer virus may infect 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.

A list of 8 types of computer viruses

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.

6 symptoms of your device being infected by a computer virus

  • Slow performance: A slow down in the computer’s processing speed is usually a dead giveaway for computer viruses. Malicious code typically hijacks computing power.
  • Device crashes and freeze-ups: System freezes and crashes are often signs of malware infection in general, but viruses can be designed specifically to cause this. While this could also be the sign of an older device, it signals an infection.
  • Missing files: Persistent pop-ups about missing files is another symptom. As you click shortcuts or try to access files, you may get notifications they no longer exist. It could be viruses deleting your important data.
  • New files appear: Beware when new files mysteriously appear. Computer viruses can delete old files and create new ones.
  • Problems with hardware or accessories: Viruses have been known to cause system changes that affect external hardware and accessories. If you can’t get that USB drive or wireless mouse to connect properly or work as it should, it could be a sign of a virus.
  • Computer performs actions on its own: If it seems your device is executing commands without your authorization, a virus could be overriding your system.

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.

Visit Bitdefender Here

Screenshot of Bitdefender website homepage with logo in the corner

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.
Screenshot of Advanced Options Windows Boot

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.

Homepage screenshot of Avast with logo

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.
Screenshot of Mac 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.

  • About 30% of American households have devices that have been infected by computer viruses.
  • According to CheckPoint, around 53% of computer viruses are spread through .exe files, with only 6% being spread through .pdf files.
  • According to Google’s Transparency Report, it removed 2.1 million malware-infected sites. Approximately 7% of all sites tested contained malware. Every week, Google detects about 50 websites containing malware.
  • Statista reports nearly 47% of computers in China are infected with malware, making it the highest infected country worldwide.
  • Kaspersky estimates that nearly there were 56 million mobile malware attacks in 2020. Android users are targeted significantly more than iOS users.

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) became the most headline-stealing form of malware.

Final Thoughts: The Danger of Computer Viruses

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.

Computer Viruses: Frequently Asked Questions

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:

  1. Slow computer performance
  2. Frequent freezes and crashes
  3. Constant pop-ups
  4. Deletion of existing files
  5. Problems with hardware

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:

  1. Install a reliable antivirus software
  2. Don’t open suspicious mail attachments
  3. Install and activate a firewall to block potentially malicious files from entering your device
  4. Use a pop-up blocker and enable your browser’s privacy settings
Leave a comment

  1. Dena Parks

    I’m sure you won’t get this message, but I’ve been hacked for 3 years or more. I have spent my savings. I’ve bought phone after phone, used different companies and they still find me. I have even got phones not in my name with different Google accounts, but they control my phone settings, steal my data and my home wifi. I’m at my wit’s end. I went months without a phone, because the stress caused heart problems. I had to take my kids phones because of this.

    • David Janssen

      We’re sorry to hear you’ve been having these issues for such a long time. In a normal case, we would advise you to set up new and unique passwords for all accounts you’re using, as you can read about here. A full return to factory settings on your devices could help as well, although without knowing how exactly the attacker keeps getting access to your devices this is a mere guess. We would advise you to seek help from someone in your surroundings who is tech-savvy and who can figure out what’s going on without you having to share too much personal information online. Perhaps the articles in the cybercrime and malware sections of our website could give you some further ideas. All the best of luck!

  2. Tabitha

    This webpage was by far one of the most interesting and informative sites I have been on in a long time!!! Thanks guys for all the information and links. Happy surfing


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