Your host is awful. Get a new host now. If your host can't even clean off your computer then they aren't a host worth having.
Change your password to something long you've never used before, a bunch of letters uppercase and lowercase, numbers, and symbols. The longer, the better. Use a trusted FTP. Make sure all input fields on your site have been properly cleaned for any sort of injection attack. Clean off YOUR personal computer, you may have a keylogger on it.
But mainly, just get a new host.