What to do if you think your computer has malware

You can check for malware yourself using the security tools already built into Windows or Mac, or by running a separate scanning program. The built-in tools are free and work without installing anything new. If you find something, the scanner will usually remove it automatically or give you the option to delete it.

The fastest way is to run a full system scan, which takes 15 minutes to an hour depending on how much is on your computer. You do not need to restart your computer first, though restarting after the scan finishes is a good idea. If your computer is running very slowly or acting strange, a malware scan is one of the first things to try.

Key Takeaways

  • Windows Defender (built into Windows 10 and 11) and Activity Monitor (on Mac) can scan for malware without you installing anything.
  • A full system scan takes 15 minutes to an hour and should run while you use your computer normally.
  • If the built-in scanner finds something, it will usually quarantine or delete it automatically.
  • Malwarebytes and Kaspersky are separate programs that catch threats the built-in tools sometimes miss, and both have free versions.
  • After removing malware, change your passwords and check your bank and email accounts for unauthorized activity.

How to scan with Windows Defender on Windows 10 or 11

Windows Defender is already running on your computer and checking files as you use them. To run a full scan that checks everything, open the Start menu and type "Windows Security" into the search box. Click the Windows Security app when it appears.

Once Windows Security opens, click "Virus & threat protection" on the left side. Under "Current threats," you will see a button that says "Scan options." Click it. Select "Full scan" from the list, then click "Scan now." The scan will start immediately and show you a progress bar. You can use your computer while it scans.

When the scan finishes, Windows Defender will show you a summary. If it found anything, it will say "Threats found" and list what it removed or quarantined. If it says "No threats found," your computer passed the scan. Either way, restart your computer when you are done.

How to scan on Mac using Activity Monitor and Malwarebytes

Mac does not have a built-in malware scanner the way Windows does. The best free option is to download Malwarebytes for Mac, which works similarly to the Windows version. Go to malwarebytes.com, click "Free download," and follow the installer. Once it is installed, open Malwarebytes and click "Scan" to start a full system scan.

If you want to check what is running on your Mac before installing anything, open Activity Monitor (search for it in Spotlight). Click the "Memory" tab to see what programs are using the most resources. Look for anything with an unfamiliar name or something that is using a lot of memory when you are not running it. If you see something suspicious, search for the name online to find out what it is.

Activity Monitor will not remove malware, but it can help you spot it. If you find something suspicious, use Malwarebytes to scan and remove it. After removal, restart your Mac.

Using Malwarebytes as a second scanner

Malwarebytes is a separate program that catches threats Windows Defender and Mac's built-in protections sometimes miss. It is free to download and use for scanning, though the paid version runs in the background all the time. For a one-time check, the free version is enough.

Go to malwarebytes.com and click "Free download." Install it like any other program. Open Malwarebytes and click the "Scan" button. The scan takes 10 to 20 minutes. When it finishes, Malwarebytes will show you what it found. Click "Quarantine" to remove anything it detected.

Running Malwarebytes after Windows Defender or Activity Monitor is useful because different scanners catch different things. If your computer is acting very strange or you suspect a serious infection, running both scanners gives you the best chance of finding it.

What to do after the scan finds malware

If any scanner found malware, the first thing to do is let it remove or quarantine the threat. Most scanners do this automatically. After removal, restart your computer. Then change your passwords for email, banking, and any other important accounts. Use a different computer or phone to change them if possible, so the malware cannot see what you type.

Check your email account for unauthorized activity. Look at the "Last account activity" section (in Gmail, this is at the bottom of the inbox). If you see login attempts from places you do not recognize, change your password again and enable two-factor authentication if the service offers it. Do the same for your bank account — log in and check for transfers or changes you did not make.

If you found malware, it is also a good time to update your operating system and all your programs. Malware often gets in through security holes that updates patch. Restart your computer one more time after updates finish installing.

Why your computer might still feel slow after scanning

Sometimes a computer feels slow even after a malware scan comes back clean. This usually means the slowness is not from malware. Check how much free space you have on your hard drive — if it is below 10 percent full, your computer will run slowly. You may also have too many programs starting when you turn on your computer, or your hard drive may be failing.

If the scan found malware and removed it, but your computer is still slow, run the scan again. Some malware hides or comes back. If a second scan finds nothing, the slowness is probably from something else — too many browser extensions, a full hard drive, or an older computer that just needs more time to do things.

If you are not sure what is causing the slowness, restart your computer and try using it for a few days. Sometimes removing malware takes a day or two to show results as the system cleans up after itself.

Frequently Asked Questions

Can malware hide from Windows Defender or Malwarebytes?

Some malware is designed to hide from security scanners, but this is rare. Running a scan in Safe Mode (restart your computer and hold Shift while clicking restart, then choose "Troubleshoot" and "Startup Settings") can catch malware that hides in normal mode. If you suspect something is still on your computer after two clean scans, Safe Mode scanning is worth trying.

Do I need to pay for Malwarebytes to remove malware?

No. The free version of Malwarebytes scans and removes malware just as well as the paid version. The paid version runs in the background all the time and stops threats before they infect you. For a one-time scan, free is enough.

What if the scanner says it found malware but cannot remove it?

Some malware locks itself so the scanner cannot delete it. Restart your computer in Safe Mode and run the scan again — malware often cannot protect itself in Safe Mode. If it still will not remove, you may need to take the computer to a repair shop or contact the malware removal support line for your antivirus program.

Should I scan my phone for malware too?

Android phones can get malware, but iPhones almost never do. If you have an Android phone, you can download Malwarebytes for Android from the Google Play Store and run a scan the same way you would on a computer. For iPhone, malware is so rare that a scan is not necessary.

How often should I scan for malware?

If you have Windows Defender or another real-time scanner running, you do not need to scan manually very often. A scan once a month is reasonable. If your computer feels slow or you notice strange behavior, scan right away. If you download files from untrusted sources often, scanning weekly is safer.