Defender platform 4.18.26080.3: false "Antivirus turned off" alerts (fixed)
Summary
Windows Security repeatedly reported Microsoft Defender Antivirus as turned off although protection was active. This was reported by users and trade media, not yet confirmed by the vendor in the available sources. A fix is reported in platform version 4.18.26080.4, released September 17.
Symptoms
- Windows Security repeatedly shows Defender as off although real-time protection is active.
- Intune sometimes marks affected devices as non-compliant.
Affected
- Microsoft Defender Antivirus platform 4.18.26080.3
- Windows 11 devices with this platform version (as reported)
Workaround
No workaround known.
Fix
Reported as fixed in Defender platform 4.18.26080.4, released September 17. The platform update is normally delivered automatically; verify the platform version in Windows Security under Settings > About.
Recommendation
Check that managed devices have received platform 4.18.26080.4 or later. Re-evaluate devices that Intune marked non-compliant during the issue before taking action, as protection was likely active. Do not disable or reinstall Defender because of these alerts.
Reports from the community and trade media
Reports from forums, Q&A sites, Reddit and trade media – linked only, without the names of the authors; the vendor’s statement is authoritative.
- Microsoft Defender: critical update fixes false alarm on Windows 11 News · borncity.com, 18 Sep 2026
- Windows 11's Defender kept falsely saying your antivirus was off and Microsoft just fixed it News · windowslatest.com, 19 Sep 2026
- Microsoft patches Windows Defender bug that insisted your antivirus was off News · techpowerup.com, 19 Sep 2026
- Microsoft Defender false alerts fixed News · blog.toolslib.net, 25 Sep 2026
Sources
- Microsoft Defender: critical update fixes false alarm on Windows 11 News · borncity.com
- Windows 11's Defender kept falsely saying your antivirus was off and Microsoft just fixed it News · www.windowslatest.com
- Microsoft patches Windows Defender bug that insisted your antivirus was off News · www.techpowerup.com
- Microsoft Defender false alerts fixed News · blog.toolslib.net
Compiled from community reports and web research and translated with AI (Claude) – not yet confirmed by the vendor. The vendor’s statements are authoritative. Updated 2 Nov 2026, 00:36.
Where the information comes from
We continuously read the vendors’ official sources, community reports and trade media and summarise them in our own words, with a link to the source:
- Microsoft: Windows release health (Windows 10/11, Server 2016 to 2025), Windows message center, known issues of Microsoft 365 Apps (Outlook, Excel, Word, PowerPoint), Edge, Intune, Autopilot, Windows 365 and Entra Connect, Microsoft KB articles with timelines, Exchange and Windows IT Pro blogs, optionally Microsoft 365 service health and message center
- other vendors: Veeam KB, Citrix (known issues), Ubuntu and Debian (regressions), Broadcom (VMware), Fortinet, Cisco, Mozilla, Let’s Encrypt
- community (title, short excerpt and link only, without the names of the authors): Microsoft Q&A, Microsoft Tech Community (discussions), Veeam R&D Forums, Eleven Forum
- targeted web research with AI (Claude), e.g. on the updates of the month – this also finds discussions on Reddit and in forums; such entries are labelled as community reports until the vendor confirms them
- early warning from trade media (title and link only): Born’s Tech and Windows World, BleepingComputer, AskWoody, Windows Latest, Windows Central, gHacks, The Windows Club, Deskmodder, Dr. Windows, WindowsArea, Frankys Web, heise online
Summary and translation with AI (Claude by Anthropic) – without any data of visitors.
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