Your Vista computer starts from hibernation overnight

So. You work on your laptop all evening, then hibernate it. When you come down stairs in the morning it has turned itself on and is sitting waiting for you to log in. If you're lucky it is on mains power, if not it is about to run out of battery. I've also heard of people finding their laptop waking up in its case and getting rather hot.

The problem is Windows Automatic Update. If you accept the default setting of install updates automatically at 3am it wakes up at 3am to do just that. Microsoft claim it will only do this on mains power and it will hibernate again afterwards. Experience suggests it may do it on battery power and may not turn off.

I suspect the problem is restarting after update. For a while MS managed to make most updates install without a restart but now most require one (more about this here). I assume that when the laptop powers up after the restart it has forgotten it is supposed to go back to sleep. Anyway, change the automatic update settings to download updates automatically and notify you but don't install. The added benefit is that you can avoid updates you don't want, like new versions of Internet Explorer and nagware like Windows Genuine Advantage. I also don't generally install updates till Windows Secrets has passed them as not likely to break your software.