The Messenger service is nothing to do with Windows Messenger. Confusing, but true.
The one causing the hassle is used in corporate networks to allow announcements to be sent to users. If you are not on such a network, there's not much point in having it turned on. The service has been around a LONG time, but these spammers latched on to it only a couple of years ago.
Go to:-
Start Menu,
Control Panel
If you see "Performance and Maintenance", select it.
Administrative tools
Services.
In the box that pops up, double-click on the line for "Messenger".
Press the "Stop" button to stop the thing arriving now, then change the "Startup type" to "Disabled" to make sure you don't see them after a reboot.
Press OK to get things remembered, then close the windows you've opened.
Job Done
