Windows Defender currently has a serious bug, that stops and detects only a small number of files a few seconds after running a fast scan or a full scan.
This problem exists in Windows Defender 4.18.1907 and later, which was released earlier this week. Microsoft is understood to have introduced this bug. when fixing another problem in July 2019 Patch Tuesday The first problem was that the system was broken.
Microsoft announced in August that it had fixed an error in the system file check, but the patch was actually delayed until users found that Windows Defender was not working properly until a patch was patched earlier this week.
This problem affects not only Windows Defender on Windows 10, but all other versions on Windows, even the same problem with Windows Defender ’ s predecessor, Security Essentials, on older versions of Windows.
However, only manual and planned scans are affected, and Windows Defender's real-time scan protection is not affected.