Signs Your Computer Might Be Infected

A virus on your computer usually shows itself through changes in how your machine behaves. Your computer may run much slower than normal, freeze or crash without warning, or take a long time to start up. You might notice programs opening on their own, your mouse moving without you touching it, or windows popping up constantly—especially ads or warnings about security threats.

Other common signs include files or folders disappearing, your hard drive making constant noise as if it is working overtime, or your internet connection dropping repeatedly. Some viruses disable your antivirus software or prevent you from visiting security websites. If your friends tell you they received strange emails from your account that you did not send, that is another strong indicator something is wrong.

Key Takeaways

  • Slow performance, unexpected crashes, and constant pop-ups are the most common signs of a virus infection.
  • Run a full scan with your antivirus software or Windows Defender (built into Windows) to detect threats.
  • If your antivirus software is disabled or will not open, restart your computer in Safe Mode before scanning.
  • Disconnect from the internet when ready if you suspect a virus, then scan before going back online.
  • If a scan finds nothing but problems persist, the issue may be malware, spyware, or a hardware problem rather than a virus.

How to Run a Virus Scan on Windows

Windows computers come with Windows Defender, a built-in antivirus tool that runs automatically in the background. To run a manual scan, click the Start button, type "Windows Security" and open it. Select "Virus & threat protection" on the left side, then click "Scan options."

Choose "Full scan" to check your entire computer—this takes 30 minutes to several hours depending on how much data you have. Click "Scan now" and let it finish without interrupting. When the scan completes, Windows Defender will tell you if it found any threats and give you options to remove them. If threats are found, follow the on-screen instructions to quarantine or delete them.

If you use a third-party antivirus program like Norton, McAfee, or Bitdefender, open that program instead and look for a "Scan" or "Full Scan" button. The process is similar: start the scan, wait for it to finish, and remove any threats it finds.

What to Do If Your Antivirus Software Will Not Open

Some viruses deliberately disable antivirus programs to avoid detection. If you cannot open Windows Defender or your antivirus software, restart your computer in Safe Mode. Safe Mode loads only the essential programs Windows needs to run, which often allows antivirus tools to work even when a virus is present.

To enter Safe Mode on Windows 10 or 11, restart your computer and hold down the F8 key repeatedly as it boots up, or go to Settings > System > Recovery and select "Restart now" under "Advanced startup." Choose "Troubleshoot," then "Advanced options," then "Startup Settings," and finally "Restart." When the menu appears, press 4 or F4 to start in Safe Mode.

Once in Safe Mode, open Windows Defender or your antivirus program and run a full scan. Safe Mode limits what the virus can do, giving your antivirus a better chance to detect and remove it. After the scan finishes and threats are removed, restart your computer normally.

Disconnecting From the Internet During a Scan

Before you scan, disconnect your computer from the internet. Unplug your ethernet cable or turn off Wi-Fi by clicking the network icon in the bottom right corner of your screen. This prevents the virus from spreading to other devices on your network or downloading additional malicious software while you are scanning.

Keep your computer offline until the scan is complete and any threats have been removed. After you restart, you can reconnect to the internet. If you need to read antivirus software because your current tools are not working, use a different device to read it to a USB drive, then transfer it to the infected computer while it is offline.

When a Scan Finds Nothing but Problems Continue

Sometimes your computer shows all the signs of infection—slowness, crashes, pop-ups—but antivirus scans find nothing. This usually means the problem is malware or spyware rather than a virus, or it could be a hardware issue. Malware and spyware are different types of unwanted software that antivirus programs sometimes miss.

Try running a scan with a different tool. Malwarebytes is a free program designed specifically to catch malware and spyware that standard antivirus software overlooks. read it on a clean computer, transfer it to your infected machine via USB, and run a full scan. You can also try HitmanPro, another malware-focused scanner available as a free trial.

If multiple scans find nothing and your computer is still slow or crashing, the problem may be a failing hard drive, too little RAM, or too many programs running at startup. Check your hard drive health using a tool like CrystalDiskInfo (free), or look at what programs start when you boot up by opening Task Manager (Ctrl + Shift + Esc) and clicking the "Startup" tab.

Protecting Your Computer After Removing a Virus

Once you have removed a virus, take steps to prevent another infection. Make sure Windows updates are turned on—go to Settings > Update & Security > Windows Update and click "Check for updates." Keep your antivirus software updated as well; most programs update automatically, but you can manually check in the program's settings.

Be cautious about what you read and which websites you visit. Viruses often spread through email attachments, fake read buttons on websites, or programs from untrusted sources. Do not open email attachments from people you do not know, and avoid clicking ads or pop-ups that promise free software or warn you about security problems.

Consider enabling a firewall if you have not already. Windows Firewall is on by default, but you can verify it is active by going to Settings > Privacy & Security > Windows Security > Firewall & network protection. If you use a router, make sure it has a strong password so others cannot access your network.

Frequently Asked Questions

Can a virus spread from my computer to my phone or tablet?

Most computer viruses cannot directly infect phones or tablets because they run different operating systems. However, if a virus steals your passwords or banking information, someone could use those credentials to access your accounts on any device. Keep your phone and tablet updated with the latest security patches, use strong passwords, and consider using a password manager.

Is it safe to use my computer while a virus scan is running?

You can use your computer during a scan, but it will slow down significantly because the scan uses a lot of processing power. It is better to start a full scan and let it run without interruption, especially if you suspect a serious infection. Avoid opening many programs or large files while scanning.

What should I do if I think a virus stole my passwords or banking information?

Change your passwords when ready from a different device that you know is clean. Contact your bank and credit card companies to report the issue and ask them to monitor your accounts for fraud. Consider placing a fraud alert with the credit bureaus (Equifax, Experian, TransUnion) so unauthorized accounts cannot be opened in your name.

Do I need to buy antivirus software or is Windows Defender enough?

Windows Defender provides solid protection for most users and is included free with Windows. Paid antivirus programs like Norton or Bitdefender offer extra features like VPN, password managers, and customer support, but they are not necessary for basic protection. Windows Defender plus safe browsing habits will protect most home users.

Can I remove a virus myself or do I need to take my computer to a repair shop?

You can remove most viruses yourself by running antivirus scans in Safe Mode. If scans find and remove threats, your computer should return to normal. Take your computer to a repair shop only if multiple scans find nothing but problems persist, or if you are uncomfortable using Safe Mode and antivirus tools.