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1Clear out junk files and repair common Windows errors2Fix the driver behind crashes, sound loss and screen glitches3Repair Windows errors before they cause bigger problemsIf Windows Defender appears not to be working in Windows 11, first check whether another antivirus provider has intentionally taken over. Then verify real-time protection, refresh security intelligence, and choose a scan suited to the problem. “Windows Defender” is commonly used to mean Microsoft Defender Antivirus; Windows Security is the app where you check its status and settings.
1. Check which antivirus provider is active
An inactive Microsoft Defender Antivirus status does not always mean something is broken. A compatible non-Microsoft antivirus product can switch Defender off while it provides antivirus protection.
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- Open Windows Security.
- Select Virus & threat protection.
- Open Manage providers and check which antivirus provider is listed as active.
If another compatible antivirus is active, that handoff may explain Defender’s status. Avoid trying to run two antivirus engines at the same time. Microsoft says Defender should return to active mode after the other antivirus product is uninstalled; check Manage providers again afterward.
2. Turn real-time protection on
If Microsoft Defender Antivirus is the provider you intend to use, check its real-time protection setting.
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- In Windows Security, open Virus & threat protection.
- Select Manage settings.
- Switch Real-time protection on.
Microsoft notes that real-time protection can be turned off temporarily and will turn back on automatically after a short while. While it is off, files you open or download are not scanned in real time, so restore the setting promptly rather than treating an off state as a fix.
3. Refresh security intelligence and Windows updates
Out-of-date security intelligence can leave protection behind. Microsoft distributes security intelligence automatically through Windows Update, and you can also check for it from Windows Security.
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- Open Windows Security and select Virus & threat protection.
- Under Virus & threat protection updates, select Protection updates.
- Select Check for updates.
If Defender protection updates repeatedly fail, follow Microsoft’s instructions for manually installing the latest protection updates. If Windows Update itself is failing, use Microsoft’s Windows 11 Windows Update troubleshooting guidance; do not assume a troubleshooter labeled for Windows 10 applies to Windows 11.
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A quick scan is a useful initial check, but it should not be treated as proof that every infection or unwanted program has been ruled out. Match the scan to what you are seeing:
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| Situation | Scan to use | What to expect |
|---|---|---|
| Routine initial check | Quick scan | A starting point for checking common locations; it is not a guarantee that no issue exists. |
| You suspect an infection | Full scan | Microsoft recommends a full scan when infection is suspected. For suspicious software, get the latest security intelligence before scanning. |
| Unwanted software persists | Microsoft Defender Offline | Microsoft recommends this escalation when unwanted software remains; the scan runs outside the usual Windows session. |
To start a scan, open Windows Security > Virus & threat protection, choose the scan options, select the scan type, and start it. Follow any prompts Windows Security displays.
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If protection updates keep failing
Use Microsoft’s manual protection-update instructions. If the underlying Windows Update service is the problem, continue with Windows 11-specific Windows Update troubleshooting rather than applying a Windows 10-only security troubleshooter.
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If malware may be interfering
Use Microsoft’s malware-removal guidance and consider Microsoft Defender Offline when unwanted software persists. Once the threat is addressed, check the active provider, real-time protection setting, and protection updates again.
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If the Windows Security app itself seems broken
The available Microsoft guidance for this issue does not establish a general Windows Security app repair or reset procedure for Windows 11. Avoid relying on an unsupported generic reset as a fix; use the relevant provider, update, or malware steps above based on the symptom you can verify.
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