A critical bug in Microsoft’s Defender Antivirus has been causing widespread confusion among Windows users. For weeks, many have received alarming alerts warning that their antivirus protection was turned off, despite it being fully functional and enabled on their systems.
The issue, which affected all supported versions of Windows client and server, including the latest Windows 11 26H1 releases, caused notifications to pop up repeatedly when users started their computers or during subsequent logins. These notifications prompted users to “Tap or click to turn on Microsoft Defender Antivirus,” even though everything was working correctly.
Microsoft acknowledged the problem in late August and has now resolved it with an update released on September 17. The company had been aware of the issue since at least June, when it first began affecting users in the Release Preview Channel of the Windows Insider program. This means that many users have been living with these incorrect alerts for months.
The bug is not unique to this particular issue. Microsoft has a history of asking customers to ignore similar errors and warnings displayed on their systems after installing updates. In April 2025, the company addressed an issue causing incorrect BitLocker drive encryption errors on Windows 10 and 11 devices. In July 2025, it fixed a bug that triggered invalid failure errors in the Windows Recovery Environment (WinRE) updates. More recently, Microsoft warned users to ignore erroneous Windows Firewall alerts caused by the June 2025 preview update.
This latest fix comes as part of a wider effort by Microsoft to address issues caused by its September 2026 security updates. The company released emergency patches earlier this week to resolve problems with Remote Desktop Services, Hyper-V, and USB audio.
While these errors may be frustrating for users, they are relatively harmless and do not compromise system security. However, they can cause unnecessary stress and anxiety, especially among those who may not be familiar with the inner workings of their systems. To avoid similar issues in the future, it’s essential to stay up-to-date with the latest updates and patches from Microsoft.
In light of this experience, users would do well to exercise caution when encountering such alerts and verify that their antivirus protection is indeed enabled before taking any action. It’s also a good idea to keep an eye on official Microsoft forums and release notes for known issues affecting Windows systems.
Source: Bleeping Computer — 2026-09-18