The latest optional update for Windows 11 may cause several issues. Microsoft had to admit earlier that the update could cause certain games to become unresponsive. Two days ago, Microsoft admitted that users might also experience a gigantic mouse cursor instead of custom ones.
Yesterday, the company confirmed that the built-in security tool Microsoft Defender Antivirus might cause a notification to be displayed that is untrue.
The app might show the notification “Microsoft Defender Antivirus is turned off” even when it is enabled and working correctly.
Microsoft writes:
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. These notifications can appear when Windows starts and intermittently afterward. They persist even if notification settings are turned off.
The issue may occur in any version of Windows and Windows Server with Microsoft Antivirus running. Microsoft says that it is investigating the issue and plans to release a fix in a future Microsoft Defender Antivirus update.
For now, there is no workaround or other option to resolve the issue. Affected users may want to ignore the notification until the issue gets fixed by Microsoft engineers.
Note that the optional update should be considered a beta release. The three confirmed issues show why. Most Windows users may want to skip them entirely, as the changes are usually included in the upcoming month’s security update for the operating system.
Whether the issues are resolved then remains to be seen. At least the RGB issue is resolved and should not affect Windows users installing the September 2026 security updates.