Microsoft Defender Scan Failures Plague Windows Systems After Security Update

Microsoft Defender users have reported widespread scan failures after a series of Security Intelligence updates began reaching Windows systems on August 18, 2026.

The issue reportedly affects Quick, Full, and Offline scans, leaving both home users and Microsoft Defender for Endpoint administrators unable to complete routine malware checks.

Aryeh Goretsky, a former ESET researcher, linked the crashes to specific Security Intelligence Update releases and Microsoft Malware Protection Engine versions 1.1.26070.7 and 1.1.26080.2.

Community testing indicates that installing Security Intelligence Update 1.457.236.0 or later restored scan functionality on many affected devices.