How to tell if your computer has a virus (and what to do about it)

2 women looking and pointing at a computer

Computer viruses have caused headaches for many of us. Some viruses brick your devices and make them impossible to use, but more often, viruses slow down your computer or steal your data. But there are steps you can take to boot a virus off your machine.

Computer viruses replicate themselves, spreading through your device’s operating system and network. The virus is also simultaneously wreaking havoc: it can damage programs, delete files, and make devastating changes to your hard drive, which can result in reduced performance. Some viruses will even crash your entire system. Viruses can also give their cybercriminal creators an opportunity to destroy or steal your sensitive data and documents.

The idea of having a virus on your computer is scary, but we’re here to help! Here we’ve gathered tips on how to prevent, detect, and defeat computer viruses.

How does a computer get a virus?

The most common reason your computer gets infected is because you downloaded or installed infected files. Pirated media and free games are common culprits, and so are phishing attacks where you click on a bad link, button, or email attachment. Once clicked, the virus or other malware installs itself. Similarly, viruses can infect your computer when you visit scam websites. Sometimes, you can unintentionally install a virus from an infected external drive, like a USB stick.

How do I tell if my computer has a virus?

If you notice any of (or all) these symptoms, your computer might have a virus:

  • Suddenly slow computer performance, meaning it takes a noticeably longer time to start up or open programs
  • Problems unexpectedly shutting down or restarting
  • Missing files
  • Frequent system crashes
  • Frequent error messages
  • Unexpected pop-up windows
  • New applications (like web browser toolbars) that appear without you downloading them
  • Overworked hard drive, which you can detect if your device’s internal fan seems to be whirring and working hard when you aren’t doing much
  • Emails that are sent automatically from your accounts without you sending them
  • Lagging web browser or your web browser constantly redirects
  • Malfunctioning antivirus programs or firewalls

What to do if your computer has a virus

If you think your computer has a virus, you should act fast to eradicate the malicious code. Don’t panic—we’ve broken down what you should do into a few easy-to-understand steps:

1. Run a full system scan

If you suspect your computer has a virus, use antivirus software to run a full system scan of your device. It’s best to set your antivirus program to do this automatically on a regular basis so you can detect any issues before they become emergencies. Review the detected threats and act—many antivirus and antimalware programs guide you through this.

2. Restore to an earlier backup

If you can’t delete the virus or infected files, try restoring your computer to an earlier backup before your problems started. Scan your system again with antivirus software and see if the same issues exist.

3. Delete temporary files

Delete the temporary files on your computer. How you delete these files is usually easy, but it depends on your operating system (like Windows or macOS). You can find detailed information if you search for your specific system.

4. Use safe mode

If you’re prevented from deleting files because your computer is malfunctioning, try booting up in safe mode. Safe mode restricts certain programs so you can work to fix the issue without interruption.

5. Reinstall your operating system

As a final measure to get rid of a computer virus, you can reinstall your device’s operating system. This can result in the loss of critical files or other data. It’s a good idea to seek professional help and take your device to a computer store. Many shops or experts will guide you through reinstalling your operating system for free.

The only way to ensure that you eliminate a virus is to wipe your device and reinstall a new operating system.

This is why you should practice good backup habits. The process (called reimaging) eliminates everything on the hard drive (both the virus files and all of your files).

Depending on the severity of the issue, you might be able to deal with malware or a virus without taking this step (by using a quality antivirus software or going into safe mode and removing bad files, for example). Still, reimaging is the most effective option if you want to be sure that the virus is removed.

There have been rare instances where a computer virus even survives reimaging. Consult a tech professional if you’re considering this drastic step.

How to prevent computer viruses

Follow these best practices to prevent viruses from infecting your devices:

1. Use antivirus software

You should always have a trusted antivirus installed on your computer—it’s best to boot up some antivirus software as soon as you start using a new device. You should be able to turn on regular scans of your entire device so you know ASAP if there are any issues.

2. Follow the core 4

By following four basic cybersecurity behaviors, you can forge good habits that make it difficult for computer viruses to get through:

  • Use complex passwords that are at least 12 characters long and are unique to each account; use a password manager to store your passwords
  • Turn on multi-factor authentication (MFA, sometimes called 2-factor authentication) for any account that permits it
  • Turn on automatic updates for your hardware, software, and apps
  • Learn how to identify phishing—don’t take the bait

3. Be careful on public Wi-Fi

Public Wi-Fi in cafes, airports, and other businesses can be convenient, but they are often unsecured and leave your phone, tablet, or computer susceptible to viruses. Using a mobile hotspot or VPN (virtual private network) is a more secure way to connect when you’re on the go.

4. Get your software fresh from the source

One of the oldest tricks in the cybercriminal’s book is to sneak viruses and malware into software and files people want to pirate. Always download software from verified sources and get your apps from your device’s official app store. You might think you’re saving money by pirating software, movies, or other media, but you’re also putting your device and network at risk.

Key takeaways

  • Prevention is key. Install and regularly update antivirus software, follow the core 4 cybersecurity practices, and be cautious on public Wi-Fi.
  • Early detection is crucial. Regularly scan for viruses and know the common signs of infection.
  • Act quickly. If you suspect a virus, isolate your device, disconnect from the internet, and run a full system scan.
  • Use reimaging as a last resort. Consider reimaging your device if other methods fail, but be prepared for potential data loss.

By taking these steps, you can enjoy a safer computer experience and protect your personal information. Knowledge is power in the fight against digital threats—so stay informed and safe online!

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