Ever get a pop up after being away from your machine for hours, offering a college degree or body part enlargements, and not know where it came from? Did the title of the window say Messenger Service? Here's how to turn off the Messenger Service.
First, as an administrative user, access the Service Explorer by going to Start, Settings then Control Panel and Administrative Tools. Next select the Services icon. Scroll through the list of services until you find Messenger.

Right-click on Messenger and select Stop. Now Right-click again on Messenger and select Properties.

Half way down the Messenger Properties window you should see Startup Type the value should read Automatic, change Automatic to Disabled.
Now your machine should be clear. Just as a matter of safety and to make you feel like you are running Win98 reboot the machine just to be safe.