And where does it say that post count is a measure of a person's reliability or legitimacy?

A spammer could make a thousand posts in a day - does he become a good member?

This member's been here since October 2008
Post count does not mean $hit!

In any case - My advice:
Secure your passwords, database, access, etc
Move to a better host. There are many of them out there that you can get a VPS off for the price of a shared hosting account (though a low-end VPS).

Ignore this guy. He stole your database. What's he gonna do now? Release it to the public? Let him. Yours is an ever growing forum.

EDIT: Ohk.. He might release the members' IP addresses and emails. You should probably email your members explaining the situation to them. Meanwhile, also ban this 'hacker'