Some systems are thrust into endless reboots after receiving Vista SP1 updates, according to messages posted to the company's support site.
Microsoft said it is investigating the reports.
Last Tuesday, Microsoft started sending Vista users two final prerequisite updates that are required before SP1 can be installed in March. The updates to the operating system's install components were delivered via Windows Updates, which automatically downloaded and installed them on the majority of Vista machines.
Users quickly started squawking.