InfoWorld reports that some Windows Vista users began finding Service Pack 1 in Windows Update

Microsoft acknowledged the error. "Yesterday, a build of SP1 was posted to Windows Update and it was inadvertently made available to a broad group. The build was intended only for our more technically advanced testers, and was meant to only be offered to those with a specific registry key set on their PC," Microsoft said in a statement. It also reiterated plans to make SP1 broadly available in mid-March.

Microsoft accidentally leaks SP1