A bug in Windows Defender creates tons of junk files

Windows Defender is a solid anti-virus solution that comes free together with every consumer-based Windows SKU. Microsoft significantly improved the quality of its anti-virus software, and it is now considered one of the best in class. Still, it is not immune to weird bugs and issues. Once, it falsely marked Winaero Tweaker as malware and now fills up users' drives with tons of junk files.


From time to time, Windows Defender performs background checks to make sure your computer is running fine and healthy. The program then stores scan history in the C:\ProgramData\Microsoft\Windows Defender\Scans\History\Store directory. Usually, that folder contains a bunch of files, taking only a few kilobytes. Unfortunately, that is not the case for some unlucky users. Some people report finding tens of thousands of temporary files. In some extreme cases, this number reaches five million, consuming more than 30GB of free space on a system drive.

Microsoft Defender ATP Banner

There are already several threads on Microsoft Forums with upset users wanting to reclaim their storage. According to numerous reports, the bug affects different Windows Versions, including the most recent and older Windows Server SKUs.

Although Microsoft is yet to confirm the problem and provide an official workaround, users have already noticed that updating the Windows Defender's engine to version 18100.6 fixes the problem. If you cannot wait for the patch to come, you can manually remove all the junk. Just be aware that you need the Administrator access level to open the Windows Defender folder. Besides, Windows hides the ProgramData folder by default, so be sure to make hidden files visible before opening it. Bear in mind that that mysterious files may come back and you may need to repeat the cleaning process until Microsoft releases a patch. Monthly patches for Windows 10 are due to arrive on May 11, so make sure to install all the updates when they become available.

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Author: Taras Buria

Taras is here to cover stories about Microsoft and everything around, although sometimes he prefers Apple.

6 thoughts on “A bug in Windows Defender creates tons of junk files”

  1. “updating the Windows Defender’s engine to version 18100.6 fixes the problem”

    “Monthly patches for Windows 10 are due to arrive on April 11”
    Surely you mean May 11.

    1. 1. We (me and Taras) assume that it was a buggy version 1.1.18100.5, and the issue is resolved in 1.1.18100.6
      2. Thanks, must be a typo.

  2. FYI You can manually update only windows Defender by going to the following site and choosing the file needed for your system.

    I was on the xxx.5 engine and was seeing the same issue with thousands of 2kb files. I searched for and found the page linked and downloaded the proper file (mpam-fe.exe). When I ran it, there was no visual confirmation of any kind but my engine version is now 1.1.18100.6 and the issue has stopped for me.

  3. Windows Update gives me error 0x80070643 , but right clicking the taskbar Windows Defender icon and selecting “Check for protection updates” works.

  4. Recently, in MS Word, when I went to save as, an INSERTED box was put into my documents that said in essence GO TO GOD or the like, plus when looking in DETAILS of the property of my documents, they have been changed from Microsoft Corporation to grizli777 ?? Can you help ?

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