Signs your computer may have a virus include sudden slowness, constant pop-ups, a browser homepage or search engine that changes on its own, unfamiliar programs, antivirus that has been switched off, and friends receiving strange messages from your accounts. If you spot these, disconnect from the internet, run a full scan, and change your passwords from a different, clean device.
10 common signs of a virus or malware
- Your computer is suddenly much slower, even when you're not doing much.
- Pop-ups and adverts appear constantly, even when your browser is closed.
- Your browser homepage or search engine changes on its own.
- New toolbars or extensions appear that you didn't install.
- Unfamiliar programs start up with Windows.
- Your antivirus or Windows Security is switched off and won't turn back on.
- The fan runs loudly while the computer should be idle.
- Friends receive odd emails or messages from your accounts.
- Files are renamed, encrypted or missing, sometimes with a ransom note. This is ransomware.
- Passwords stop working, or you get security alerts about logins you didn't make.
What to do if you think you have a virus
- Disconnect from the internet. Turn off Wi-Fi or unplug the network cable to stop the malware sending data or spreading.
- Don't log in to banking or enter passwords on the infected computer.
- Run a full scan. In Windows, open Windows Security > Virus & threat protection > Scan options and run a Full scan. For stubborn infections, choose Microsoft Defender Offline scan, which restarts the computer and scans before Windows loads.
- Remove unfamiliar browser extensions and reset your browser settings.
- Change your passwords from a different device, starting with email and banking, and turn on two-step verification.
- Check your bank statements and contact your bank straight away if you see anything unusual.
Watch out for fake virus warnings
A common scam is a pop-up claiming your computer is infected, with a phone number to call "Microsoft support". Microsoft doesn't display warnings with phone numbers, and won't call you out of the blue. Never call the number or let a caller connect to your computer. Close the browser, and if it won't close, restart the computer.
You can forward suspicious emails to the National Cyber Security Centre at report@phishing.gov.uk.
When to get professional help
- You see a ransom note or your files have been encrypted.
- The infection keeps coming back after scans.
- You've let a scammer access your computer remotely.
- It's a business computer with customer or financial data on it.
- Your security software won't run or update.
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