The automatic restart caused us no end of difficulties at my work. We were running long running data loading integration test scripts on windows boxes. Nothing worse then finding out that the script that was supposed to run over the weekend made it 8 hours then the machine rebooted to install updates.
There's a regedit/GPO that should be applied on any system like this. The key is in Local Computer Policy > Computer Configuration > Administrative Templates > Windows Components > Windows Update (under GPO), and HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\WindowsUpdate (Some place in there, I'm on 7 right now and can't find what it would be on XP).
It is particularly strange that it would happen over the weekend. Updates should be downloaded and installed only on Tuesdays, unless you set it otherwise. If your scripts are running every weekend, why not set the machines to update on Mondays?
