Microsoft is replacing the certificates that Windows PCs use to confirm they are talking to genuine Windows Update servers, and machines that miss the changeover will stop receiving updates. The company announced the rotation on October 8, and the current certificates expire on May 17 and June 19, 2027. Most users apparently won't have to do anything, since the replacements ship inside the regular monthly security updates. Windows 11 25H2 and later, including the recently launched 26H2, need no action. Windows 11 24H2 needs the September 2025 security update or newer, while other supported Win