After updates or onecare, restart automated logon

I noticed that I am not happy that when Windows Updates or OneCare updates
have completed and restart machine.

Vista Ultmate allows to auto logon administrator or administrators group.
How do I prevent that if I am away from computer and during updates and
restart itself without auto logon itself? It would serious exploit to
unauthorisation access by any users.

I checked Regedit that there is no autologon. How did Vista automatically
log on itself?

Much appreciation if you could help please?