Windows 11 includes built-in antivirus protection through Windows Security (Microsoft Defender Antivirus), and it scans your PC automatically in the background. You can also run a scan yourself anytime, whether you want a quick check, a full scan of every file, a scan of one folder or USB drive, or an offline scan that catches stubborn malware. This guide covers every scan type, when to use each, and what to do if something is found.
Quick Answer
Open Start, search for Windows Security, and open it. Click Virus & threat protection, then Quick scan. For a deeper check, click Scan options, choose Full scan or Microsoft Defender Antivirus (offline scan), and click Scan now.
Scan Types Compared
| Scan | What it checks | Time | Use when |
|---|---|---|---|
| Quick scan | Locations where threats are commonly found | A few minutes | Routine check, something seems off |
| Full scan | All files and running programs | Can take an hour or more | You suspect an infection |
| Custom scan | Files and folders you choose | Varies | Checking a download or USB drive |
| Offline scan | Scans before Windows fully starts | About 15 minutes; PC restarts | Malware that hides while Windows runs |
Run a Quick Scan
- Click Start, type Windows Security, and open it. You can also click the shield icon in the taskbar notification area.
- Click Virus & threat protection.
- Click Quick scan.
Results appear on the same page when the scan finishes.
Run a Full, Custom, or Offline Scan
- In Virus & threat protection, click Scan options.
- Select one:
- Full scan for the entire PC.
- Custom scan, then click Scan now and choose a folder or drive.
- Microsoft Defender Antivirus (offline scan), which restarts your PC. Save your work first.
- Click Scan now.
Scan a File, Folder, or USB Drive From File Explorer
Right-click the item in File Explorer and choose Show more options > Scan with Microsoft Defender. On some versions, the option appears directly in the right-click menu.
Run a Scan From PowerShell (Advanced)
Open Terminal (Admin) and run:
- Quick scan:
Start-MpScan -ScanType QuickScan - Full scan:
Start-MpScan -ScanType FullScan - Offline scan:
Start-MpWDOScan
Update Protection Before Scanning
In Virus & threat protection, scroll to Virus & threat protection updates, click Protection updates, and then Check for updates. Current definitions help detect the newest threats.
If a Threat Is Found
- Windows Security usually quarantines or removes it automatically.
- Click Protection history to see what was found and the action taken.
- Choose Remove or Quarantine if an action is still needed. Only choose Allow if you are sure the file is safe.
- Run a full or offline scan afterward to make sure nothing else remains.
- Change passwords for important accounts if you suspect data was exposed, using a different, clean device if possible.
Make Sure Protection Is On
Under Virus & threat protection settings, click Manage settings and confirm Real-time protection, Cloud-delivered protection, and Tamper protection are on. If you installed another antivirus program, Windows Security may show that product as the active provider instead; use that program to scan.
Troubleshooting
Windows Security will not open
Restart the PC and install Windows updates. If it still fails, go to Settings > Apps > Installed apps, find Windows Security, and use Advanced options > Reset.
Scan options are grayed out
Another antivirus may be active, or your organization manages security settings.
Full scan takes forever
This is normal on large drives. Let it finish, or run a quick scan plus a custom scan of specific folders.
Frequently Asked Questions
Is Windows Security enough protection?
For most home users, built-in protection combined with updates and safe browsing habits is solid. Some people add another security product for extra features.
How often should I scan manually?
Windows scans automatically. Run a manual scan when something seems wrong or after downloading files from an unfamiliar source.
Can I schedule scans?
Yes, with Task Scheduler. Open it, go to Task Scheduler Library > Microsoft > Windows > Windows Defender, and edit the Windows Defender Scheduled Scan task.
Summary
- Open Windows Security > Virus & threat protection.
- Click Quick scan for a fast check.
- Use Scan options for full, custom, or offline scans.
- Check Protection history and keep protection updates current.
Kermit Matthews is a freelance writer based in Philadelphia, Pennsylvania with more than a decade of experience writing technology guides. He has a Bachelor’s and Master’s degree in Computer Science and has spent much of his professional career in IT management.
He specializes in writing content about iPhones, Android devices, Microsoft Office, and many other popular applications and devices.