A known issue causing false warnings about Defender Antivirus being disabled has been fixed by Microsoft. The company announced the resolution through its Windows release health dashboard on Thursday, confirming that the fix arrived in Microsoft Defender Antivirus version 4.18.26080.4, released on September 17.
Microsoft first acknowledged the problem in late August, though users in the Windows Insider program's Release Preview Channel had been experiencing it since at least June. The defect impacted all currently supported versions of Windows client and server systems, spanning from Windows 11 26H1 through Windows Server 2025.
The bug manifested as misleading notifications within the Windows Security app, urging users to "Tap or click to turn on Microsoft Defender Antivirus." According to Microsoft's statement, "After installing the latest updates for Microsoft Defender Antivirus, notifications might appear stating that 'Microsoft Defender Antivirus is turned off,' even though the antivirus is functioning correctly and all settings show it as active." The company noted that "These notifications can appear when Windows starts and intermittently afterward. They persist even if notification settings are turned off."
This incident represents another instance of Microsoft releasing updates that generated spurious error messages requiring user attention. In April 2025, the vendor addressed incorrect BitLocker encryption alerts on Windows 10 and Windows 11 machines and corrected a flaw producing invalid 0x80070643 errors following Windows Recovery Environment updates.
During July 2025, Microsoft instructed users to disregard false Windows Firewall warnings appearing after reboots following the June 2025 preview update. The following month brought warnings about incorrect CertificateServicesClient errors triggered by the July 2025 preview and subsequent Windows 11 24H2 releases.
This week, Microsoft also deployed emergency patches addressing Remote Desktop Services, Hyper-V, and USB audio problems introduced by the September 2026 security updates.