Microsoft Defender bug may fill your hard drive with thousands of files


Level 5
Jul 21, 2017

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.


Level 40
Jan 9, 2020


Level 48
Content Creator
Apr 24, 2016
Fix is planned for tomorrow:

Defender modul version: 1.1.18100.5 is the bad one, upcoming 1.1.18100.6 the good one (y)
Yes, but I'm still on 1.1.18100.5 😭 and no update offered through Windows Update.


Level 33
Apr 1, 2019
Yes, but I'm still on 1.1.18100.5 😭 and no update offered through Windows Update.
Same here. Meanwhile the folder hasn't grown today, but I haven't run any scans today.


Level 14
Jan 21, 2018
For a comparison this screenshot is from a PC where I installed Win 10 on a new partition on 25.04.21. Soon afterwards I installed F-Secure SAFE on it, so I believe that these files were created up until the point where I set SAFE as the AV.

Defender Store files 2nd - 06.05.21.PNG
From the same PC, from the the old OS install partition where I had again used SAFE as the AV, there are a few more files and they are from a longer period, but only going back to January 2021 although the OS had been installed in August 2020

Defender Store files 1st - 06.05.21.PNG