Completely and correctly scanning your computer for viruses and other malware like Trojan horses, rootkits, spyware, adware, worms, etc. is often a very important troubleshooting step. A "simple" virus scan will no longer do.
Many forms of malware cause or masquerade as seemingly unrelated Windows and PC issues like Blue Screens of Death, issues with DLL files, crashes, unusual hard drive activity, unfamiliar screens or pop-ups, and other serious Windows problems, so it's important to properly check your computer for malware when working to solve many problems.
Note: If you can't log in to your computer, see the section toward the bottom of this page for help.
How to Scan Your Computer for Viruses, Trojans, and Other Malware
- Download and run the Microsoft Windows Malicious Software Removal Tool. This free, Microsoft provided malware removal tool won't find everything, but it will check for specific, "prevalent malware," which is a good start.
Note: You may already have the Malicious Software Removal Tool installed. If so, make sure you update it using Windows Update so it can scan for the latest malware.
- Update your anti-virus/anti-malware software installed on your computer.
Before running a complete malware/virus scan, you need to make sure the virus definitions are up to date. These regular updates tell your antivirus software how to find and remove the latest viruses from your PC.
Tip: Definition updates usually happen automatically but not always. Some malware will even specifically target this feature as part of its infection! Look for an Update button or menu item to start the check-and-update process for your antivirus program.
Important: Don't have a virus scan program installed? Download one now! There are several free anti-virus programs available, like AVG and Avast, so there's no excuse for not running one. On that note - stick to just one. It might seem like a good idea to run multiple antivirus programs at once but in reality that usually causes problems and should be avoided.
- Run a complete virus scan on your entire computer. If you happen to have another non-persistent (not always running) antimalware tool installed, like SUPERAntiSpyware or Malwarebytes, run that too when this is done.
Note: Don't simply run the default, quick system scan which may not include many important parts of your PC. Check that you're scanning every part of every single hard drive and other connected storage device on your computer.
Important: Specifically, make sure any virus scan includes the master boot record, boot sector, and any applications currently running in memory. These are particularly sensitive areas of your computer that can harbor the most dangerous malware.
Can't Sign in to Your Computer to Run a Scan?
It's possible that your computer is infected to the point that you can't effectively log on to the operating system. These are the more serious viruses that prevent the OS from launching, but there's no need to worry because you have a couple options that will still work to get rid of the infection.
Since some viruses are loaded into memory when the computer first starts up, you can try booting into Safe Mode if you're using Windows. That should stop any viruses that automatically load when you first sign in, and let you follow the steps above to get rid of them.
Note: Be sure to start Windows in Safe Mode with Networking if you haven't yet downloaded the tool from Step 1 or don't have any antivirus programs installed. You'll need networking access to download files from the internet.
Another option for scanning for viruses when you don't have access to Windows is to use a Free Bootable Antivirus Program. These are programs that run from portable devices like discs or flash drives, that can scan a hard drive for viruses without starting the operating system at all.
More Virus & Malware Scanning Help
If you've scanned your entire computer for viruses but suspect that it may still be infected, try a free on-demand virus scanner next.
These tools are great next steps when you're pretty sure that your computer still has an infection but your installed antivirus program didn't catch it.
An online virus scan with tools like VirusTotal or Metadefender, is yet a further step you can take, at least in situations where you have a good idea what file(s) may be infected. This is less likely to be the thing that fixes the problem but worth a shot as a last resort - it's free and easy to do.
Tip: One way to speed up the scanning process is to delete temporary files so that the anti-malware program doesn't have to scan through all that useless data. Though it isn't common, if the virus is being stored in a temporary folder, then doing this might even remove the virus right away before you start the scan.