Microsoft is investigating reports that some Windows 11 devices are failing to boot with "UNMOUNTABLE_BOOT_VOLUME" errors after installing the January 2026 Patch Tuesday security updates. [...]

Microsoft has released emergency, out-of-band updates on Saturday for Windows 10, Windows 11, and Windows Server to fix an issue that prevented Microsoft Outlook classic from opening when using PSTs stored in cloud storage. [...]

A cyberattack targeting Poland's power grid in late December 2025 has been linked to the Russian state-sponsored hacking group Sandworm, which attempted to deploy a new destructive data-wiping malware dubbed DynoWiper during the attack.. [...]