Why is desktop computer waking up?

I found my wife's Windows XP desktop powered up this morning. She had placed
it in hibernate just before midnight last night. I searched around and found
that the WindowsUpdate.Log file that had been modified in the wee hours. If
I am interpreting this correctly it seems automatic update (AU) took the
computer out of hibernation at 1:00 AM and then something did (or did not)
happen at 3:00 AM. The machine then stayed on. I looked at Control
Panel|Automatic Updates and sure enough it was set for automatic download at
3:00 AM (I think this was set up during Windows XP installation).

Question: Is Windows Update supposed to turn the computer on for any reason?
I thought that during hibernate NOTHING was running -- and certainly not the
CPU checking the time. Is this happening via the NIC?

I'll obviously take updates out of automatic.

Here are the pertinent log entries:

2005-09-11 23:56:18 684 5bc AU
AU found 0 updates for install at shutdown

2005-09-11 23:56:18 1064 438 Misc
=========== Logging initialized (build: 5.8.0.2469, tz: -0700)=====

2005-09-11 23:56:18 1064 438 Misc
= Process: C:\WINDOWS\Explorer.EXE

2005-09-11 23:56:18 1064 438 Misc
= Module: C:\WINDOWS\system32\wuaueng.dll

2005-09-11 23:56:18 1064 438 Shutdwn
Install at shutdown: no updates to install

2005-09-11 23:56:22 684 124 AU
AU received hibernate event

2005-09-12 01:00:38 684 124 AU
AU received wakeup event

2005-09-12 01:00:39 684 124 AU
AU received wakeup event

2005-09-12 03:00:10 684 124 AU Forced
install timer expired for scheduled install