There have been numerous threads posted on the forum about site hacking, here is one way you can minimize it. Please check your Anonymous FTP settings. Go to your hosting account control panel, look for Anonymous FTP, and turn it off... like now! This is a major security hole and most hosting providers have this enabled by default.
Bluehost and other hosting providers have started issuing warnings about this setting, and it is a change that many simply are not aware of or overlook. Maybe this will help someone out there.