I know this is an old topic and sorry for bringing it back up but I just despise threads like this, posted by people who obviously know nothing about hackers. I have a few points to make:
1) Hackers create, a webmaster is a form of hacker for example.
2) Its Crackers that destroy, so the a holes who mess up your site are crackers.
3) If that has happened to your site your host has &$^! security.
4) I would suggest looking at server logs to fins out who they are, even the best leave traces.