Microsoft Fixes Windows Defender Crash Breaking Antivirus Scans

Microsoft resolved a Windows Defender issue that caused quick and full antivirus scans to fail on some Windows 10 and Windows 11 systems, with users reporting msmpeng.exe crashes, WinDefend service timeouts, and 0xc0000005 access violation errors alongside messages stating "Threat service has stopped. Restart it now". Administrators said the failures appeared across multiple devices rather than isolated endpoints, indicating a product-wide fault tied to a recent Defender update or security intelligence release.

Reports from system administrators showed the problem spread widely enough that some customers reinstalled operating systems while troubleshooting. Microsoft confirmed the bug and said it was fixed through Microsoft Defender Antivirus security intelligence update 1.457.236.0 or later, advising affected users to install the latest Defender signature updates through Windows Update; some admins had also circulated a temporary workaround involving removal of dynamic signatures and forcing a signature refresh.