viruses and malware:

Check for and remove viruses and malware

1. A virus, malware, or other malicious software could cause your PC to run slowly. Some other symptoms include unexpected pop-up messages, programs that unexpectedly start automatically, or the sound of your hard disk constantly working.
2. The best way to handle viruses and malicious software is to try to prevent them by running antimalware and antivirus software and keeping it up to date. Even if you take precautions, your PC can still become infected.

You can scan your PC for viruses or other malicious software by using Windows Defender, which is included in Windows 10. For more info, see Protect your PC.

Note
If you’re using other antivirus or antimalware software, check the documentation for that program to learn how to scan for viruses. Also, make sure multiple antivirus programs aren’t running at the same time. If they are, pick the one you want to run, and then disable or uninstall any others.

To scan for viruses using Windows Defender

1. Select the Start button > Settings > Update & security > Windows Defender > Open Windows Defender.
2. Select the Update tab > Update Definitions to make sure you have the latest definition file.
3. Select the Home tab > Scan Now, then wait for Windows Defender to finish scanning for viruses and malware.
4. Do one of the following, depending on the results of the scan:
5. If Windows Defender finds a virus or malware and can’t remove or quarantine it, contact Microsoft Support for help.
6. If no viruses are found, restart your PC and try to reproduce the performance problem you were having with your PC.

Note

If Windows Defender doesn’t open, can’t update the definition file, or can’t finish scanning for viruses, try running Windows Defender in Offline Mode, which is explained in the following procedure.

To scan for malware and viruses with Windows Defender Offline

Save any documents or anything else you might have open on your PC.
Select the Start button > Settings > Update & security > Windows Defender > Scan Offline.
Try to reproduce the performance issue.
If your PC still runs slowly, continue to the next tip.