Spam You Didn't Send
You probably have a virus on at least one of the computers you use.
Also, anyone whom the virus emailed.... ( everyone that was in your email addressbook.... ) who then clicked on the link in the spam email.... may also now have that same virus.
Here's how to Fix it:
(1) Disinfect ALL of the computers you have used in the last six months. All you need is the FREE version of the anti-virus program you can get at: http://www.malwarebytes.org
(2) Then, immediately change ALL of your online passwords (including your email, like AOL, Gmail, Yahoo, Hotmail, and your online banking, etc.) FROM A KNOWN VIRUS-FREE CLEAN computer.
Good luck.
PS - Feel free to bookmark this page of instructions ( this page: http://brucewagner.posterous.com/spam-you-didnt-send ) and then email this link to anyone who gets afflicted with a spam virus like this in the future.
Questions? I'm happy to help.
Bruce Wagner
646-719-9000