Don’t you hate it when it does that? Especially when you’re playing a game and it gets you killed. When you leave your computer on overnight to download a big file and it reboots on you.  Well, no more!

Go to Start->Run->gpedit.msc

Go to Local Computer Policy-> Computer Configuration->Administrative Templates->Windows Components->Windows Update

Find “No auto-restart with logged on users for scheduled automatic upd…”->Right Click->Properties->Click Enables->Ok

(Click for bigger image)

No more auto-restarts! This was tested on Windows XP SP3.