How to Check for Malware and Viruses on Windows 11

Windows 11 includes Microsoft Defender Antivirus in the Windows Security app. You can run a quick scan in seconds, a full scan for a deeper check, or an offline scan for stubborn threats.

Quick Answer

Open Start, type Windows Security, go to Virus and threat protection and click Quick scan. For a deeper check, click Scan options and choose Full scan or Microsoft Defender Offline scan.

How to Check for Malware on Windows 11

1. Click Start, type Windows Security and open it.
2. Select Virus and threat protection.
3. Click Quick scan to check common locations.
4. For a thorough check, click Scan options, choose Full scan and click Scan now.
5. If you suspect a hidden threat, choose Microsoft Defender Offline scan. The PC restarts and scans before Windows loads.
6. Review results in Protection history and follow the recommended actions.

Scan Types

Scan	Use it when
Quick scan	Routine check (a few minutes)
Full scan	Something seems wrong (can take an hour or more)
Custom scan	Checking one folder or drive
Offline scan	Malware resists removal

Related: adding a Defender exclusion safely.

Signs You Might Have Malware

• Pop-ups when no browser is open, or new toolbars and extensions.
• Browser home page or search engine changed without you.
• Unknown programs in Task Manager > Startup.
• Security settings turned off that you didn’t change.

Scan one file, folder, or USB drive

1. Open File Explorer and find the item.
2. Right-click it. On Windows 11 you may need to select Show more options first.
3. Choose Scan with Microsoft Defender. Windows Security opens and shows the result.

This is the quickest way to check a download before you open it.

What to do if a threat is found

1. Select the threat in Windows Security and choose Remove or Quarantine, then Start actions.
2. Run a Microsoft Defender Offline scan to catch anything that hid during the first scan.
3. Uninstall any programs you don’t recognize in Settings > Apps > Installed apps.
4. Change passwords for important accounts from a device you know is clean, and turn on two-step verification.
5. If problems continue, back up your files and use Settings > System > Recovery > Reset this PC.

Keep protection switched on

In Windows Security > Virus & threat protection > Manage settings, make sure Real-time protection, Cloud-delivered protection, and Tamper Protection are on. Leave SmartScreen enabled too; it warns you about unknown downloads and websites (see SmartScreen settings in Windows 11). If you install another antivirus, Microsoft Defender steps aside automatically and turns itself back on if you remove it.

Review Protection History

Windows Security keeps a record of everything it has found. Open Windows Security > Virus & threat protection > Protection history to see recent detections, what action was taken, and whether anything still needs your attention. Items marked as quarantined have been isolated and can’t run.

Get a Second Opinion From Microsoft

If you suspect something was missed, Microsoft offers the free Microsoft Safety Scanner, an on-demand tool you download and run separately from Defender. Download it only from Microsoft’s website; each download works for a limited time, so get a fresh copy whenever you need it. It doesn’t replace real-time protection.

For a specific infection, see how to remove a Trojan from Windows 11.

Troubleshooting

• Scan button greyed out: another antivirus may be installed and in control. Scan with that product instead.
• Browser still shows pop-ups: reset the browser and remove unknown extensions.
• Signs of infection after scans: back up your files and consider resetting Windows.
• Related: testing files in Windows Sandbox and troubleshooting Windows 11.

Frequently Asked Questions

Is the built-in antivirus enough?

For most home users, Microsoft Defender plus updates and care with downloads gives good protection.

How often should I scan?

Defender scans automatically. Run a manual scan if something seems off.

Can I scan one file?

Yes. Right-click it and choose Scan with Microsoft Defender (under Show more options on some builds). Adware sometimes leaves a root certificate behind, and the guide on removing certificates from Windows 11 shows how to find and delete it.

What about scam pop-ups?

Close the browser. Never call numbers shown in pop-ups.

Summary

1. Open Windows Security.
2. Go to Virus and threat protection.
3. Run a Quick scan.
4. Use Full or Offline scan if needed.
5. Check Protection history.