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If you are using a device with Microsoft's Windows 10 operating system and Windows Defender as the default security solution, you may be impacted by a bug that is filling the hard drive with files.

Windows Defender puts thousands of files in the folder C:\ProgramData\Microsoft\Windows Defender\Scans\History\Store if a device is affected by the issue. More than 10,800 items were placed in the folder on a test system running Windows 10 version 20H2. Other users reported over 950,000 files over the course of a 24 hour period and 30 Gigabytes of storage occupied by the files. Most files are small in size, between 1 and 2 Kilobytes.

The bug may affect certain operations, such as synchronization or backup tasks. Backups and syncs may take longer to complete, and may occupy more space. Storage devices may also be filled up quickly, depending on the severity of the experienced issue on a device.

Several Microsoft Answers threads exist in which Windows users and server administrators report the issue. It is affecting a wide variety of Windows versions, and not only Windows 10 according to these reports. Windows versions mentioned include Windows Server 2021 R2, Windows Server 2016 and 2019, and Windows 10.

Since it is a Windows Defender bug, it is likely that all Windows versions may be affected by the issue. In other words, it does not depend on the operating system but the Windows Defender version.

The affected engine version is 18100.5, the fixed engine version appears to be 18100.6. You can verify the version of Windows Defender on Windows 10 by opening Settings > Update & Security > Windows Security > Open Windows Security > Settings icon > About. Microsoft may release the fixed version this Thursday.

One workaround at the time of writing is to delete the files that are in the folder. Note that new files will be added to the folder by Windows Defender until the issue is fixed by an update. Some users reported that turning off realtime protections will also stop the production of the files.

Note that you need administrative rights to open the folder, and that some folders may be hidden by default.

To sum it up:

• Windows Defender has a bug that places lots of files into the folder C:\ProgramData\Microsoft\Windows Defender\Scans\History\Store.
  
• Microsoft will release a fix soon for the issue.
  
• The files can be deleted.
  

Now You: Are you affected by the issue?
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