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1Repair Windows errors before they cause bigger problems2Scan for outdated or missing drivers - takes under a minute3Clear out junk files and repair common Windows errorsIf Windows 11 keeps telling you to turn on virus protection while Microsoft Defender looks switched on, you may be seeing a false alert that Microsoft has documented. Microsoft says it fixed the problem in Defender Antivirus update 4.18.26080.4, released September 17, 2026. The fix is a Defender update, so you don’t need to buy another antivirus product.
What Microsoft says is happening
Microsoft’s Windows 11 release-health page describes the issue as “Incorrect notifications that ‘Microsoft Defender Antivirus is turned off’.” Microsoft’s wording is: “After installing Microsoft Defender Antivirus update (version 4.18.26070.9), released on August 5, 2026, 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.”
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The details that matter:
- The alert could appear at startup and then intermittently.
- It could keep appearing even after notification settings were turned off.
- It isn’t tied to one Windows 11 release. Microsoft says it can occur on any version of Windows or Windows Server running Defender Antivirus with the latest Defender updates. Its affected list includes Windows 11 23H2, 24H2, 25H2 and 26H1.
- The resolution is Defender update 4.18.26080.4 (released September 17, 2026). Microsoft marked the issue resolved on September 30, 2026.
The exact “Turn on virus protection” wording is what users report in threads such as this Microsoft Q&A question. Microsoft’s notice uses slightly different wording, so treat the match as likely, not certain. Check your own protection state to confirm.
How to fix it
1. Confirm that protection is really on
- Open Start, type Windows Security, and open it.
- Select Virus & threat protection.
- Look for a status without warnings. Then open Manage settings and check that Real-time protection is on.
For a more exact check, open PowerShell and run:
Get-MpComputerStatus | Select-Object AntivirusEnabled, RealTimeProtectionEnabled, AMProductVersion
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If both settings return True, Defender is working and the alert is probably the false one.
2. Update Defender
- In Windows Security, go to Virus & threat protection.
- Under Virus & threat protection updates, select Protection updates, then Check for updates.
- You can also run Settings > Windows Update > Check for updates.
- Restart the PC, because the alert was known to show at startup.
Microsoft names 4.18.26080.4 as the fixing release. Later versions may supersede it, so the version you have should be that number or higher. The AMProductVersion value from the command above shows which one you have.
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3. Don’t rely on turning notifications off
Microsoft says these incorrect alerts could persist even with notification settings off. Muting them won’t fix the cause, and it could hide a real warning later.
4. If it still appears after updating
Microsoft lists Feedback Hub and Get Help (or Microsoft Support) as the channels for reporting it. Include your Windows version, your Defender version and, if it helps, a screenshot of the alert.
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When the alert is real
The documented defect applies only when Defender works correctly and every setting shows it active. If Windows Security shows protection as off, or the Defender service has stopped, you have a different problem. Follow current Microsoft support guidance for that case and don’t assume the alert is false.
Another possible cause is a third-party antivirus program on the PC. Windows normally turns Defender’s active protection off when another product takes over, so a prompt in that situation may be legitimate. Microsoft’s notice doesn’t cover this case.
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