How to Properly Scan Your Computer for Malware

Rid your computer of Trojans, viruses, spyware & more

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.

Laptop scanning for malware
vladwel/iStock

If you can't log in to your computer, see the section toward the bottom of this page for help.

Time Required: Properly scanning your PC for viruses and other malware is easy and could take several minutes or longer. The more files you have, and the slower your computer is, the greater the time the scan will take.

How to Scan Your Computer for Viruses, Trojans, and Other Malware

Applies To: These are general steps to scan and remove malware from your PC and should apply equally to Windows 10, Windows 8 (including Windows 8.1), Windows 7, Windows Vista, and Windows XP.

Should you back up your files before running a virus scan? See the section at the bottom of this page for a discussion on that.

  1. 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.

    Microsoft Windows Malicious Software Removal Tool screenshot
    Microsoft Windows Malicious Software Removal Tool.

    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.

    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. Although 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.

  2. Update your anti-virus/anti-malware software installed on your computer.

    Avast Internet Security update option
    Avast Internet Security.

    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.

    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.

    Don't have a virus remover installed? Download one now! There are several free anti-virus programs available, like AVG and Avast, and many that can be used on a trial basis at no cost, so there's zero 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.

  3. 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.

    SUPERAntiSpyware screenshot
    SUPERAntiSpyware.

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 devices on your computer.

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 threats that automatically load when you first sign in, and let you follow the steps above to get rid of the viruses.

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.

Stinger virus scanner screenshot
Stinger.

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.

VirusTotal scan results
VirusTotal.

If the virus doesn't seem to want to be removed with our suggestions, consider disconnecting from the internet so that the malware can't communicate with a remote server to further infect your computer. Just make sure that if you do this, to first download and update anything related to the antivirus program, and then disconnect only during the duration of the virus scan.

Not sure if you should quarantine, delete, or clean the virus? Follow that link for more information on what those terms mean. You might regret permanently deleting a "virus" if it's actually a harmless, false alarm.

You also always have the ability to erase your whole hard drive and start over fresh with a new operating system, but do this only if you can't remove the virus from your computer. For obvious reasons, wiping the hard drive clean will erase all of your files. However, it is a solid method of getting rid of viruses that can't seem to be cleaned with antivirus tools.

Should You Back Up Before Running Virus Scans?

Backing up your computer before a scan might sound helpful. After all, you don't want your important documents, videos, photos, etc. to be removed along with the viruses.

While backing up can be useful before a virus scan, be extra careful what you're backing up. The last thing you want is to save all your computer files in a backup and then erase the viruses, only to have them remain in the backup and return upon a restore!

Unfortunately, unless you know exactly what on your computer is infected, you won't know what's safe to back up and what's better left on your computer for the malware scan.

Something you can do to ensure that your most important files are backed up is to copy just those things to an external hard drive or back them up online, but leave the majority of your files where they are. It's unlikely that the virus scan alone will corrupt your files anyway.

Another way to look at this is to back up anything you want and then run a virus scan on your computer. Should something be found, take note of which files are infected and then delete or scan the backed up files, too, to ensure that the threats are gone from both the originals and the backups.