Pixelhum

Windows XP Service Pack 2 has a habit of rebooting the computer if Windows Update is scheduled to install updates automatically. This can result in lost data if you have unsaved work on your screen at the time.

Tim Rain has written a good article explaining why this all happens, how Windows determines whether to restart, and how to prevent AU from automatically rebooting.

Obviously, if Windows Update needs to reboot the computer then it should be rebooted as soon as possible, but this at least allows some control and prevents data loss.