Microsoft Investigates Boot Failures in Windows 11 After January 2026 Update

Microsoft Investigates Boot Failures in Windows 11 After January 2026 Update

First seen 26 Jan 2026, 06:42 UTC BleepingcomputerCybersecuritynews 34.8

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Microsoft is investigating critical boot failure issues affecting Windows 11 devices after the January 2026 security update, specifically the KB5074109 cumulative update. Users have reported encountering 'UNMOUNTABLE_BOOT_VOLUME' errors on devices running Windows 11 versions 25H2 and 24H2, preventing their systems from starting properly.