Windows Defender users complain about bug that creates tens of thousands of files

A bug in Windows Defender is causing some users to see tens of thousands of files appearing in a folder on their C drive for no reason. Some users complain that it takes up gigabytes of storage space.

The problem occurs on all kinds of different Windows devices, according to several users on the Microsoft forum. They see the files appearing on both Windows 10 computers and Windows Servers, both versions 2016, 2019 and 2021 R2. The bug seems to be due to Windows Defender, specifically with engine version 1.1.18100.5.

Due to an unknown problem in that software, Defender puts tens of thousands or even hundreds of thousands of files in C:ProgramDataMicrosoftWindows DefenderScansHistoryStore. One user says he sees 400,000 files, another even 950,000. These are files of one or two kilobytes in size, but together they take up gigabytes of space on disks. According to the affected users, this also causes problems with creating backups.

Microsoft says on the forum that it is aware of the problem. A fix will follow later on Thursday.