Microsoft has released a fix for a bug in Windows Security that incorrectly reported the Microsoft Defender Antivirus as disabled. The issue was addressed in the Defender platform update version 4.18.26080.4, which was deployed on September 17.
The update installs automatically for most users. Manual intervention is only required if mandatory security updates have been restricted via Group Policy or the Registry Editor. The bug caused false alerts to appear during system boot and at random intervals.
The company officially acknowledged the problem on August 28, noting that it impacted all supported versions of Windows and Windows Server running recent Defender updates. Users in the Windows Insider program reported encountering these warnings as early as June.
Clicking on the false notification redirected users to the Windows Security home tab, where the antivirus status was correctly displayed as active. Microsoft did not identify a specific update responsible for the error, as Defender updates are distributed on a daily basis.
