First thing do a system scan with your updated AV. Viruses hijacking address books, and replicating forged e-mails to the established contacts has been around for a long time. It resurfaces every once in a while.

DA

hmmm...was it your email contacts or maybe your Facebook contacts? I've read of a lot of problems that way with Facebook.

I'm with damccoy on this one...sounds like it could be a virus infection.

well what contact list? makes a world of difference here. If it is an email address book that would be very different than if it was a facebook contacts list.

we must have more complete info about what is happening and in what program and give us the specific name if it is an email program and what version of windows you are using.

no it is very doubtful that just redoing the list will fix the problem especially if it is acutally hacked or if it is infected.

the first thing to do is go to some other computer and change all your passwords and do not use some simple word for a password that is easy to break, use a combo of letters and numbers to create a strong password. NEVER use a real word. IF you do it on that same computer if it has been hacked then they will likely know the new password so always do this on some other pc.
Create strong passwords