To turn it off completely and for good do as follows:
1. Go into Control Panel > Administrative Tools > Services.
2. Highlight the service called "Automatic Updates". You will know when you have the correct one because you will see a description about it telling you what it does.
3. Right click once highlighted and click stop to terminate the service.
4. Right click on it again and go to Properties. Half way down the first tab there is "Startup Type:" change this to disabled.
Congratulations. You have now disabled Automatic Updates service. Not only will this make certain the service won't run, but by disabling it properly you are freeing up system resources as they won't be diverted to running a service that you don't use.