My e-mail account was hacked. Now everyone in my address book is getting messages from me that I didn't send.?

Change your password to your email account. Inform everyone that got a email that you did not send, that it's not yours. Make the password unpredictable. Change into another email address, and transfer your contacts. It's not a virus. But if you want to be on the safe side, you can try wiping out your computer and resetting it to the default, to eliminate any viruses you may think that the computer has. All in all, change your email's password or switch to another email account. Make sure your security questions are up to date. Also if you have gmail, it will tell you your last account activity. And if you have yahoo, it will also say if an unknown device accessed your account. If you have neither of those, I suggest you switch to any of those two. Because many reports of being hacked are coming from people who use AOL, hotmail etc