Microsoft has finally fixed a bug that was causing incorrect alerts to pop up on users’ screens, warning them that their Defender Antivirus software had been turned off. This issue had been affecting users of various Windows versions, including the latest Windows 11 and Windows Server releases, since at least June.
The problem arose after installing recent updates for Microsoft Defender Antivirus, which triggered erroneous alerts in the Windows Security app. These notifications would appear when Windows started up or intermittently afterward, even if notification settings were turned off. The alerts prompted users to “Tap or click to turn on Microsoft Defender Antivirus,” despite the software functioning correctly and all settings showing it as active.
This is not an isolated incident for Microsoft. In recent months, the company has asked customers to ignore incorrect errors and alerts displayed on their systems after installing updates. For example, in April 2025, Microsoft addressed an issue that was triggering incorrect BitLocker drive encryption errors on Windows 10 and Windows 11 devices. Similarly, in July 2025, the company fixed a bug that caused invalid 0x80070643 failure errors after installing the Windows Recovery Environment (WinRE) updates.
The latest fix for the Defender Antivirus issue was included in the Microsoft Defender Antivirus update version 4.18.26080.4, released on September 17. This update resolves the problem affecting all supported Windows client and server versions, including the latest Windows 11 26H1 and Windows Server 2025 releases.
Microsoft’s repeated issues with incorrect alerts and errors have raised concerns about the reliability of its software updates. While it is understandable that occasional bugs slip through the cracks, this frequency of problems suggests a deeper issue with Microsoft’s testing and validation processes. Users should be cautious when receiving error messages after installing updates and verify the accuracy of these warnings before taking any action.
In light of these repeated issues, users are advised to exercise caution when dealing with error messages and alerts after installing software updates. If you receive an alert warning that your antivirus is turned off, check your system settings to confirm that it is still active. Additionally, keep an eye on official Microsoft communication channels for notifications about known issues and patches, and adjust your update schedule accordingly to minimize the risk of encountering these problems.
Source: Bleeping Computer — 2026-09-18