How to Scan Computer for Malware

How to Scan Computer for Malware

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.

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 Computer for Malware

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.

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.

A. 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.

B. 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.

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

A. 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.
B.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.

C. 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.

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.
A. 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.
B. 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.

How to Scan Computer for 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.

How to Scan Computer for Malware

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.

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.

How to Scan Computer for Malware

What Is Malware?
Malware, a shortened combination of the words malicious and software, is a catch-all term for any sort of software designed with malicious intent.
That malicious intent is often theft of your private information or the creation of a backdoor to your computer so someone can gain access to it without your permission. However, software that does anything that it didn't tell you it was going to do could be considered malware.
Malware is sometimes called badware and is often used synonymously with many of the common types of malware, listed below.
In legal documents, malware is sometimes referred to as computer contamination so if you ever see that, it's just a fancy way of saying malware.

What are Common Types of Malware?

Though some of these terms can be used to describe software with a legitimate, non-malicious intent, malware is generally understood to exist in one or more of the following forms:

• Virus: Infects program files and/or personal files

• Spyware: Software that collects personal information

• Worm: Malware that can replicate itself across a network

• Trojan horse: Malware that looks, and may even operate, as a legitimate program

• Browser hijacker: Software that modifies your web browser

• Rootkit: Software that gains administrative rights for malicious intent

• Malvertising: The use of legitimate online advertising to spread malicious software.

How to Scan Computer for Malware

There are other types of programs, or parts of programs, that could be considered malicious due to the simple fact that they carry a malicious agenda, but the ones listed above are so common that they get their own categories.

Some types of adware, the term for advertisement-supported software, are sometimes considered malware, but usually only when those advertisements are designed to trick users into downloading other, more malicious, software.

How Does a Malware Infection Happen? 

Malware can infect a computer or other device in a number of ways. It usually happens completely by accident, often times by way of downloading software that is bundled with a malicious application.

Some malware can get on your computer by taking advantage of security vulnerabilities in your operating system and software programs. Outdated versions of browsers, and often their add-ons or plug-ins as well, are easy targets.

Most of the time, however, malware is installed by users (that's you!) overlooking what they're doing and rushing through program installations that include malicious software. Many programs install malware-ridden toolbars, download assistants, system and Internet optimizers, bogus antivirus software, and other tools automatically... unless you explicitly tell them not to.

Another common source of malware is via software downloads that at first seem to be something safe like a simple image, video, or audio file, but in reality is a harmful executable file that installs the malicious program.

See the How Do You Protect Yourself From a Malware Infection? the section below for help on preventing these types of infections from happening in the first place.

How to Scan Computer for Malware

How Do You Remove Malware?

Aside from the most serious of malware infections, most are removable with some simple steps, although some are easier to remove than others.

The most common types of malware are actual programs like the legitimate software you use every day. Those programs can be uninstalled, just like anything else, from Control Panel, at least in Windows operating systems.

Other malware, however, is more complex to remove, like rogue registry keys and individual files that can only be removed manually. These types of malware infections are best removed with anti-malware tools and similar specialized programs.

How Do You Protect Yourself From a Malware Infection?

Obviously, the smartest way to avoid malware is to take precautions to prevent the malware from infecting your computer or device in the first place.

The most important way to prevent malware from reaching your computer is by making sure you have an antivirus/antimalware program installed and that you have it configured to constantly look for signs of malicious activity in downloads and active files.

Check out our always-updated Best Free Antivirus Programs list if you don't have one and aren't sure which one to choose.

Beyond software that automatically keeps an eye out for malware, the most important thing you can do to protect your computer is to change your behavior.

One way is to avoid opening email and other messaging attachments from people or organizations you don't know or don't trust. Even if you do know the sender, make sure that whatever is attached is something you were expecting or can follow up about in another message. One clever way malware is spread is by auto-mailing copies of itself to friends and family in an email contact list.

How to Scan Computer for Malware