If you have a up-to-date security program, like McAfee, I would run a FULL SCAN. It may detect the intruding program and quarantine it. However, depending on how sophisticated the hacker is, security may not isolate it.
Secondly, you should bring up your ISP account (on AOL, you can click on "Help" at the top of the screen and choose "Manage My Account") and change your password. The hacker may have already done this, so it might take some doing to find out what the password is now. I would advise that you change your email address as well; down side to that is you will need to notify everybody with whom you communicate of your new address.
And, I would contact your ISP and notify them that your account has been hacked.