If Microsoft Defender is not currently active, the following procedures serve as the functional equivalent of "installing" active protection.
If the Defender binaries are corrupted or missing due to system errors or malware tampering, a repair installation is required. This involves using the System File Checker (SFC) and Deployment Image Servicing and Management (DISM). install windows defender windows 10
| Issue | Likely Cause | Resolution | | :--- | :--- | :--- | | "Windows Defender is turned off by Group Policy" | Organizational policy or registry setting. | Run gpedit.msc and disable the "Turn off Microsoft Defender Antivirus" policy. | | "Threat Service has stopped" | Service crash or corruption. | Restart the WinDefend service in services.msc or run sfc /scannow . | | "Page not available" in GUI | Corrupted App Package. | Run the Reset-AppxPackage PowerShell command detailed in Section 4.2. | | Green checkmark persists after uninstalling AV | Leftover "Security Provider" registry keys. | Run a specialized removal tool provided by the previous AV vendor. | If Microsoft Defender is not currently active, the