i presume you made an account and were you using windows live messenger?
If you receive the message about being logged in from a different location, then you probably gave. I used Windows live messenger on my desktop and laptop and once the desktop signed in, a message popped up on my laptop saying that i was logged in at two locations. Ask if anyone has used you computer in your home. You or someone must have made an account for you to be able to use the live chat service.