Originally Posted by MediaGuy

Yeah this happened to me before... you were hacked. You have to change your wordpress password, your FTP password, and get the host to run a virus software.

Then, clear your FTP client's xml/cache of passwords. You'll have to re-enter them as you log in to your sites again. The exploit actually jumps in on the client's FTP access attempt as you do an upload. Lots of wordpress sites compromised this way, according to a GoDaddy tech support guy I talked with once...

Good luck!

:D