Our verdict: Microsoft Safety Scanner is a simple, trustworthy second scan using the same detection data as Microsoft Defender. It needs no installation and leaves nothing behind. Each copy stops working after 10 days, it has no real-time protection, and the download is large.
About Microsoft Safety Scanner
Microsoft Safety Scanner (msert.exe) is a free scan tool from Microsoft that finds and removes malware from Windows PCs and tries to reverse changes made by detected threats. It is a single portable file: it does not appear in the Start menu, and you remove it by deleting the file.
The scanner ships with the current Microsoft security intelligence update, so each download is valid for only 10 days. After that, you download a new copy. It offers quick, full and custom scans and writes a detailed log to %SYSTEMROOT%\debug\msert.log. Microsoft recommends Microsoft Defender Antivirus for continuous protection.
What it does well
- Quick, full and custom scans. Choose how much of the PC to scan before you start.
- Defender detection data. Uses the same security intelligence as Microsoft Defender Antivirus.
- Change reversal. Tries to undo changes that detected malware made to the system.
- Portable. Runs from a single file and is removed by deleting it.
- Detailed log. Writes all results to msert.log in the Windows debug folder.
Who it is for
Good fit
Anyone who wants a quick second scan from Microsoft without installing another security product.
Look elsewhere
People looking for always-on protection or a scanner they can keep on a USB stick for months.
Pros and cons
Pros
- Official Microsoft tool, no account and no ads
- Portable, leaves nothing installed
- Uses up-to-date Defender detection data
Cons
- Each download expires after 10 days
- Large download of over 200 MB
- No real-time protection and only basic options
How to install Microsoft Safety Scanner
Download the 64-bit file for Windows 10 or 11, run msert.exe and pick a scan type; a full scan can take a long time on large drives. Check the result screen and the msert.log file. Delete the file afterwards and download a fresh copy for the next scan, because each copy expires after 10 days.
Questions about Microsoft Safety Scanner
Is Microsoft Safety Scanner free?
Yes. Microsoft provides it free of charge for Windows PCs.
Why does it stop working after 10 days?
Each copy contains the detection data current on the day you download it. Microsoft limits it to 10 days so that you always scan with recent definitions.
Do I need it if I have Microsoft Defender?
Usually not. Defender already uses the same detection data. The scanner is useful as an extra one-off scan or when Defender cannot run properly.
