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Microsoft resolves incorrect Defender Antivirus alerts | brief

Scworld • September 21, 2026

Coverage from Bleeping Computer indicates that Microsoft has addressed a bug causing false alerts that Microsoft Defender Antivirus was disabled. This issue affected users across supported Windows client and server versions.

The problem, which surfaced in the Windows Insider program as early as June and was acknowledged by Microsoft in late August, led to erroneous notifications in the Windows Security app. These alerts incorrectly stated that Microsoft Defender Antivirus was turned off, despite the software functioning correctly. Microsoft has now resolved this issue with an update to Microsoft Defender Antivirus, version 4.18.26080.4, released on September 17.

This is not the first time Microsoft has had to issue guidance to users regarding incorrect alerts following software updates. Previously, the company addressed similar issues with BitLocker encryption errors, Windows Recovery Environment failures, Windows Firewall alerts, and certificate enrollment errors. Additionally, Microsoft recently released emergency updates to fix problems with Remote Desktop Services, Hyper-V, and USB audio that stemmed from September security updates.

Source: Bleeping Computer

SC Staff September 1, 2026

SC Editorial Intelligence , expert reviewed August 27, 2026

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This article is one source in a clustered incident — the cluster page carries the summary, timeline and every other outlet covering it.

Microsoft Resolves False Alerts in Defender Antivirus Microsoft has fixed a bug that caused incorrect alerts indicating that Defender Antivirus was turned off after recent updates. This issue affected users across all supported Windows client and server versions, including Windows 11 26H1 and Windows Server 2025. The bug was first acknowledged in late August and had been impacting users since at least June, particularly those in the Windows Insider program. The erroneous notifications prompted users to activate Defender Antivirus despite it functioning correctly. Microsoft released an update (version 4.18.26080.4) on September 17 to address this issue. This is not the first instance of Microsoft dealing with incorrect alerts following updates, as similar issues have occurred with BitLocker, Windows Firewall, and certificate enrollment errors. Additionally, emergency updates were released to fix other issues related to Remote Desktop Services and USB audio. Users are advised to apply the latest updates to avoid confusion from these alerts. 2 sources 27

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Platforms (2)

Microsoft Defender Antivirus Windows