Sounds like you got some kind of spyware infection or you hotmail got hijacked. Go to a another computer and change your password and security questions. Do a full scan of your system with a good AV like NOD32 to be sure your system isn't infected with anything. You can use the free NOD32 on line scanner at
http://www.eset.com/onlinescan/
Have you allowed any third party companies to access your Hotmail account from Facebook or any place like that to transfer e-mail address or add people to a service?