The reason why the forums were hit was they have a high popularity and were vulnerable. Almost every forum software has a vulnerability. I am guessing the other forums got SQLI or Socially Engineering into giving information for someone to update their forum or something to that effect. Other than that the pastebin gives you information. As a digital forensic investigator, I can tell you this happens quite often from the lack of knowledge of the forum administrator. Clearly the admin or admins of caraudio.com are competent with their security.