Resolved Question: My email is sending out spam messages, how can I stop?

I noticed this morning before work that my hotmail email account was being spammed and was sending out spam messages to my entire contacts book. I know the address that was sending the message. What can I do to prevent this from happening. I left my computer on at home with the virus scanner running a full scan, and yes I turned off my net connection so it wont happen again while its doing this? What else can I do to stop this? Is it something as simple as changing my password or something?