User id in my contact list are receiving spam from my Hotmail account.Spam being sent via my hotmail address to all in my contact list

Hello every one , I am using an hotmail email account and since past few days I am facing alot of problem with this. The problem is that i am continuously getting returned undeliverable mail with my email address as the sender and also all the contacts that are there in my address book are receiving spam from my hotmail adress. I just cant figure out why and how this is happening. Is there any virus that has attacked my account which is sending the spam to all the user id in the password or its something else . Please can someone help me to solve this problem

As my hotmail account and address book are stored on MSN servers, how did this happen? Is there a virus on the MSN servers stealing my address book and using my account to send spam. This has happened over 7 times within the past 4 days! I have since changed my password and scanned for keyloggers/spyware on all of the PC's that I have used to access hotmail.