Installed Update took nearly 8 hours to shut down the machine.

I tried to shut my machine down around 1:40pm ET on 6/3/13 and there was the little exclamation mark indicating there was one critical update waiting to install when I shutdown the machine. I come back over 7 hours later and the machine is still trying to shut down while installing this critical update. I hit the power button, but the computer came right back on with its shutdown/installing...