PC hijacked for spamming

I'm pretty certain my PC (at least my hotmail account) has been captured and my computer (or maybe just my hotmail account) is beiing used to send out virus-infected spam to complete strangers. I received a virus alert response from a contact that was not in my address book, saying that I had sent him a virus-infected e-mail from my hotmail account. Could you advise me what I should do? Is the problem on my PC (surprising since I use zonealarm) or should I just change my hotmail password asap?

 

Hi,

Scroll right down to the bottom of the page of your post. Check out some of the "similar threads". My email address was used in the same manner as yours. I got some nasty replies.
I have since closed that email address down, Baz