Do Son 
According to a support document published by Microsoft, installing the latest updates for Microsoft Defender Antivirus may cause the system to display frequent notifications claiming that Microsoft Defender Antivirus has been turned off.
The trouble is that the notification appears repeatedly regardless of whether Microsoft Defender has actually been disabled. Worse still, even after a user switches off the notification settings, these alerts persist as stubbornly as ever.
Nearly Every Version Is Affected
As detailed on Microsoft’s release-health dashboard, the issue can be observed on virtually any version of Windows or Windows Server running Microsoft Defender Antivirus with the latest Defender updates. The affected releases include:
- Windows 11 26H1
- Windows 11 25H2 / 24H2
- Windows 11 23H2
- Windows 10 22H2 / 21H2
- Windows 10 LTSC 2019 / 2016
- All versions of Windows Server 2012 through 2025
Microsoft Will Push an Update Once Fixed
At present, Microsoft is investigating the cause of the problem and formulating a remedy. Once the fix has been finalised, the company will deliver the solution through automatic updates. In the meantime, users of Microsoft Defender may simply disregard the erroneous notifications the system throws up. After Microsoft ships its fix, these alerts should vanish on their own.
This issue is unrelated to the monthly Windows 11 cumulative update, and uninstalling that update will not resolve it.
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