Microsoft Fixes False Defender Antivirus Disabled Alerts

Microsoft resolved a Windows Security defect that falsely reported Microsoft Defender Antivirus as disabled even though the service and its protections were functioning normally. The issue affected supported Windows 10, Windows 11, and Windows Server systems, first surfacing among Windows Insiders in June before appearing more broadly after a Defender update in early August.

The misleading alerts could appear at startup and intermittently afterward, could not be permanently dismissed, and persisted despite notification-setting changes. Microsoft released the correction in Defender Antivirus version 4.18.26080.4 on September 17; it installs automatically unless mandatory security updates have been blocked through Registry or Group Policy settings.