Windows Defender Bug Fills Hard Drive

John Lister's picture

A bug with Windows Defender has been filling computers with thousands of largely useless files. The bug is fixed with the latest update and this is definitely an application worth keeping updated.

Windows Defender (officially known as Microsoft Defender Antivirus) is the built-in security tool in Windows 10. The consensus view is that it's not as good as the best third-party tools, but does a decent job and is certainly a useful line of defense for the average user.

Unfortunately a recent update, which took Windows Defender to version 1.1.18100.5, introduced an annoying bug. Users noticed a problem with a file folder located on most machines at C:\ProgramData\Microsoft\Windows Defender\Scans\History\Store, which may need administrator privileges to access.

30GB Of Unwanted Files

This folder should contain a few files which relate to previous scans. There's not a great deal users can do with them as they aren't in a format accessible by other applications. Generally the files are a couple of kilobytes at most and thus users can safely ignore them.

The problem is that on some machines literally thousands of the files have been generated. In the most extreme case reported they totaled 30GB. As Bleeping Computer notes, that could be a significant problem for people who use a small drive for Windows and programs and a larger one for documents and data. (Source:

Update Should Fix Problem

The good news is that the problem appears to be fixed with a new update taking Windows Defender to version 1.1.18100.6. Windows Defender should keep itself automatically updated, but users can check which version they have by clicking on the cog icon for Settings within the Windows Security tool. (Source:

If necessary, users can manually trigger an update through the Windows Update tool by looking for an update listed as "Security Intelligence Update for Microsoft Defender Antivirus."

It's not yet clear whether the fix in the update will clear out the unwanted files. If not, it appears safe to carry out a full scan in Windows Defender then empty the C:\ProgramData\Microsoft\Windows Defender\Scans\History\Store folder. However, users may want to take a backup of the files to an external drive and keep it safe for a few days until they are certain Windows Defender is still running normally.

What's Your Opinion?

Have you spotted this problem? Do you pay much attention to Windows Defender? Should Microsoft warn users of such bugs or is it simpler just to concentrate on fixing them through updates?

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