Microsoft’s January 13, 2026 cumulative security update—KB5074109 (OS builds 26200.7623 and 26100.7623)—has triggered a wave of stability problems across a wide range of Windows 11 devices, including black screens, failed boots, Remote Desktop authentication errors, and application hangs. While Microsoft lists multiple fixes and mitigations in the official KB article, real‑world reports from users and independent outlets show the update has produced severe side effects on certain hardware...