How do I stop Microsoft Updater from being God of my computer?

I downgraded from Windows Vista to XP a few years back because of this problem. The computer would constantly update without my approval and there was no way to change it. Since having XP again, I regained control and was able to choose when the computer decided to do computer updates. However, in the last 6 months, some of their updates once again took the control out of my hands and I find it updating without asking me. It also starts updating when I log off every night, which I do not want it doing without my consent. It also has started to place me at the user log in screen when I start up, which it did not do before. It used to go directly to desktop. How do I get Microsoft to stop playing God over my computer?