Fixed in September 2026: false Defender 'AV off' alert

Call: Deploy. This is the September list of minor problems that are already fixed and weren’t security issues. It’s here so the next person searching for the error finds the answer.

Defender says it’s turned off. It isn’t.

• What broke: After Defender platform update 4.18.26070.9 (August 5), Windows kept showing “Microsoft Defender Antivirus is turned off” notifications. Antivirus was running the whole time. The notifications were cosmetic, but they were persistent, which is the worst kind of cosmetic.
• Who was hit: Windows and Windows Server with the current Defender platform. That’s broad, but the impact was noise and help-desk tickets, not lost protection.
• How it was fixed: Defender platform 4.18.26080.4, released September 17. Microsoft marked the issue resolved on September 30. If a machine still shows the warning, check its platform version (Get-MpComputerStatus, AMProductVersion) and update it.

Sources: Windows release health (opens in a new tab)↗⁠.

Sources

• https://learn.microsoft.com/en-us/windows/release-health/status-windows-11-25h2⁠↗ (opens in a new tab)