spams in hotmail

recently i just re created a new hotmail address, and i only add a couple of friends on the msn.

 

i never key in my hotmail address in any website or used it before.

 

and yet i am recieving some junk mails , i wonder how the hell the spammer got my email address?

 

and i doubt my friends are infected.

 

can anyone share some discussion on how this spam email thing spread about? thanks