Microsoft resolves bug that caused Windows Defender antivirus scans to fail after a few seconds

Windows Defender 'Quick' and 'Full' scans failed, leading to numerous complaints

Microsoft has resolved an issue in Windows Defender tool that caused the antivirus scans run by the utility to fail after a few seconds.

The company said the issue has been resolved in "Security Intelligence Update for Windows Defender Antivirus - KB2267602 (Version 1.301.1684.0)" definitions.

A large number of Windows 10 users had complained about the glitch in the past two days in Microsoft tech support forums, Reddit, as well as many tech support sites. The users said that Windows Defender "Quick" and "Full" antivirus scans stopped within seconds after scanning just a handful of files. Normally, those examine thousands of files and take several minutes or even hours to complete.

According to BleepingComputer, the flaw affected Windows Defender version 4.18.1908.7 (KB4052623), which was released earlier this week. It also impacted other Windows versions that are shipped with Windows Defender tool, as well as Microsoft Security Essentials (MSE), Windows Defender's precursor on earlier Windows versions, such as Windows 7.

Microsoft introduced this bug while trying to fix another flaw, which was introduced with the July 2019 Patch Tuesday. That original bug broke the system file checker command "sfc /scannow" that allows Windows users to scan and fix corrupt files. It caused the Windows System File Checker utility to incorrectly flag some of Windows Defender's internal files as corrupt. It also showed error message stating that "Windows Resource Protection found corrupt files but was unable to fix some of them".

The error message caused many system admins to believe that there was some issue with their Windows Defender tool and its updates.

In August, Microsoft said it was releasing Windows Defender 4.18.1908.7 to fix the bug, but the patch was delayed. Finally, when the patch was released earlier this week, it didn't yield the results that Microsoft was expecting from it.

According to Microsoft, only scheduled or manual scans were impacted by the bug. Performing a Custom Scan would have resulted in normal scan of the files, as specified by the user.