You login to a server to do some work and you are greeted by the dreaded Windows Update countdown timer.  It seems like it's picked the most inconvenient time of day when in actuality, it won't restart when the computer is locked and now that you've unlocked it, it's counting down.

As I've hinted above, you can lock the console and postpone the restart.  Or you can do one of two things:

Open a command prompt and enter the following: 

NET STOP WUAUSERV

or

You can open services and stop the Automatic Updates service.

The restart will be instantly postponed and it won't return until you either restart the computer or restart the service.