Microsoft Patches Windows Defender Bug That Insisted Your Antivirus Was Off

Microsoft has fixed the bug that made Windows Security wrongly claim Microsoft Defender Antivirus was turned off. According to Windows Latest, the fix comes in Defender platform update 4.18.26080.4, which Microsoft released on September 17. No manual action is needed, and the update should arrive on its own unless you have blocked mandatory security updates through Group Policy or the Registry Editor. The false alert usually showed up when Windows booted up, then returned at random, even with notifications turned off. Apparently, clicking it only opened the Windows Security home tab, where everything showed as active.

Microsoft acknowledged the problem on August 28 and said it affected any supported version of Windows or Windows Server running the latest Defender updates. It never named the update responsible, and since Defender updates ship daily, there is no single KB to roll back to. Windows Insider users have apparently been seeing similar warnings since at least June. TechPowerUp covered the alert when it first surfaced, and several of our own staff ran into it too. Notably, almost three weeks passed between Microsoft's confirmation and the fix, which seems slow for a bug this visible.