This is a "messenger" question?

there are many ways this goes on, since your login is stored into the system advertisement bots can grab your login name and spam it up. You can also enter into chat rooms and thus your name is released into the system. And there is a "find contact" button in MSN. So yes, you can be looked up. You could download some third party privacy plugins, but i discourage this as it can lead to viruses.

Hope this helped :D

Under messenger in preferences go to ignore list and check "ignore those not on my list. This will stop people from bothering you that you do not know.

Your one friend willl have told all there friends about u and they will have added u simple

explanation

people ramdumly search, just delete, or denie them