Windows Defender bug creating thousands of files on Windows 10 systems
If you’ve found your system running unexpectedly short of storage space over the past couple of days, then Windows Defender could be to blame.
Some users report that the bug has led to hundreds of thousands and even millions of files being generated by the security software, taking up gigabytes of storage space.
The problem affects systems that use Windows Defender as the default security solution and appears to be caused by engine version 18100.5. The problem has reportedly been addressed in 18100.6 and you can check to see which version of Defender you’re running by going to Settings > Update & Security > Windows Security > Open Windows Security > Settings > About.
The files are being stored in C:\ProgramData\Microsoft\Windows Defender\Scans\History\Store\ so you should check there to see if you have the issue.
Users on Microsoft Answers have discussed the problem with one person reporting that 4 million files -- weighing in at over 11GB -- were generated overnight on their Windows Server 2019 disks. Other Windows Server versions have been similarly affected.
A number of users also report running Sophos, so it’s possible that could be contributing to the issue.
Over at Ghacks, a test system running Windows 10 version 20H2 saw over 10,800 files created overnight.
Aside from updating Defender, the other workaround is to delete the files and turn off real-time protection, but of course that may leave your system vulnerable in the meantime.