Microsoft Safety Scanner (MSERT) is a free malware removal tool designed to find and eliminate viruses, spyware, and other malicious software that may have evaded your primary antivirus. This guide shows you how to download, run, and interpret results from Microsoft Safety Scanner.
When to Use Microsoft Safety Scanner
- Second opinion: Your PC feels slow or behaves strangely despite having antivirus
- Malware blocking installation: Some viruses prevent new antivirus installation - MSERT requires no installation
- Offline machines: Download on a clean PC, transfer via USB to infected machine
- Post-cleanup verification: Confirm your system is clean after removing malware
Step 1: Download Microsoft Safety Scanner
- Go to the official download page:
- Select your version:
- 64-bit: Most modern computers (recommended)
- 32-bit: Older machines (pre-2015)
- Locate the file:
- The download is named
msert.exe - It's a portable application - no installation required
- The download is named
Warning: Only download from Microsoft's official website. Never use third-party download sites.
Step 2: Run a Scan
- Double-click msert.exe
- Click Yes on the User Account Control prompt
- Accept the license agreement and click Next
- Click Next on the welcome screen
- Choose a scan type: (see details below)
- Click Next to start scanning
- Wait for completion - don't close the window
- Review results and restart if malware was removed
Scan Types Explained
| Scan Type | What It Scans | Duration | When to Use |
|---|---|---|---|
| Quick Scan | Memory, registry, startup folders, system folders | 5-10 minutes | Routine check or if PC is acting slightly odd |
| Full Scan | Every file on all hard drives | 1-10+ hours | Deep infection, after Quick finds malware, thorough cleanup |
| Custom Scan | Quick Scan + specific folder you select | Varies | Scanning USB drives or external media |
Recommendation: Start with Quick Scan. If it finds malware, follow up with a Full Scan to ensure complete removal.
Understanding Scan Results
No Threats Found
Your system is clean according to Microsoft's definitions. Consider running Windows Defender or your primary antivirus for additional verification.
Threats Found and Remediated
Safety Scanner detected and removed malware. Review what was found and restart your computer to complete the cleanup.
Threats Found But Not Removed
Some malware may require manual intervention or boot into Safe Mode to remove. Consider running the scan in Safe Mode or using Windows Defender Offline.
The 10-Day Expiration Rule
Microsoft Safety Scanner has a built-in 10-day expiration:
- After 10 days, the tool stops working
- This ensures you always use current virus definitions
- Delete the old
msert.exeand download fresh when needed
Best practice: Download a new copy each time you need to scan rather than keeping an old version.
Safety Scanner vs. Windows Defender
| Feature | Windows Defender | Safety Scanner |
|---|---|---|
| Protection type | Real-time (always on) | On-demand (manual) |
| Updates | Automatic via Windows Update | Manual (re-download) |
| Installation | Built into Windows | Portable (no install) |
| Conflicts | May conflict with third-party AV | Works with all AV software |
| Offline use | Needs internet for updates | Can scan offline machines |
Advanced: Command-Line Usage
For IT administrators, Safety Scanner supports command-line parameters:
msert.exe /Q # Quiet mode (no UI)
msert.exe /N # Detect only, don't remove
msert.exe /F # Force full scan
msert.exe /F:Y # Full scan, auto-cleanLog file location: C:\Windows\debug\msert.log