A recent update released by Microsoft for the Windows Defender engine earlier this week breaks down the manual scanning feature of the antivirus on Windows systems.
The update, which increases the engine version to 4.18.1908.7, was supposed to correct a System File Checker error that a previous update introduced as part of the July 2019 rollout.
The glitch originally caused a sfc /scannow check to incorrectly flag Windows Defender components as corrupted, and the update released this week was supposed to fully resolve this unexpected behavior.
But as reported by Gunter Born, the new update actually breaks down the manual scanning feature of Windows Defender, as the antivirus is no longer able to complete quick and full scans initiated by users. The automatic scans that Windows Defender performs regularly were not affected.
The bug affected not only Windows Defender on Windows 10, but also on Windows 8.1. Microsoft Security Essentials, which is available for Windows 7 devices and uses the same engine as Windows Defender, was impacted as well.
“Fix already available”
Most users report that after beginning a system scan, the process ends prematurely, with only a handful of files scanned. Custom scans of all hard-disk contents worked correctly though.
Microsoft has already acknowledged the problem and confirmed the issue only affected manual scan options, explaining that real-time protection and automatic scans worked as expected.
The company has released a fix as part of Security Intelligence version 1.301.1684.0, and users are recommended to install it as soon as possible.
To check this version in Windows Defender and look for updates, follow this path:
Windows Defender > Virus & threat protection > Virus & threat protection updates > Check of updates
At the time of writing this article everything should work correctly on devices where the latest Security Intelligence update was installed.