Windows 11 shutdown bug forces Microsoft into out-of-band damage control

Microsoft has rushed out an out-of-band Windows 11 update after January's Patch Tuesday broke something as fundamental as turning PCs off.

The emergency fix, KB5077797, landed on January 17 for Windows 11 version 23H2 and is aimed squarely at cleaning up the mess left behind by the regular monthly update earlier in the month. That update, intended to close a long list of security holes, instead left some systems stubbornly refusing to shut down, restart, or hibernate, with shutdown commands frequently shrugged off by the operating system.

The culprit turned out to be System Guard Secure Launch, one of Microsoft's boot-time hardening features, which didn't play nicely with the January update.

On affected systems – typically builds where Secure Launch is enabled by default – machines would go through the motions of shutting down, then either sit there humming away or spring back to life. That translated into laptops ...