Microsoft has acknowledged an issue affecting PCs after a mandatory security update in January, resulting in a new variant of the black screen of death. The crashes are linked to devices that did not successfully install the December 2025 security update and became unresponsive when attempting to roll back the update. Microsoft is working on a partial resolution to prevent further no-boot scenarios, but this fix will not stop devices from entering the problematic state or restore functionality to those already affected. The issue primarily impacts commercial devices running Windows 11 KB5074109 (25H2 Build 26200.7623 and 24H2 Build 26100.7623). Affected users experiencing the Black Screen of Death with the UNMOUNTABLEBOOTVOLUME error will need to manually recover their computers using the Windows Recovery Environment (WinRE).