It would be worth running an antivirus scan on your computer to ensure that there isn't any keylogging software installed which could allow hackers to discover your login/FTP details. Also it would be worth checking the
website hosting affected for any files which could be used by hackers to gain entry to the
website hosting. If other
website hostings aren't affected then I'm inclined to think that the hackers have found away into your
website hosting rather than the server.