If you where hacked you'll need to patch your forums, make sure you're using stock files (and that they haven't been altered by a hacker), and make sure your webspace doesn't have malicious files lingering around which would allow a remote hacker to continue compromising your system.
I actually just did a cleanup of a really nasty hack last week, they aren't pretty and you as the owner are really responsible for hosting these files; after a while Google and antivirus people will start flagging your site as malicious and users will start getting warnings about your site hosting malicious content if you allow it to just sit there.
You should look into either hiring someone to fix your site, or if you think you can do it yourself (which I highly advise against as with disaster recovery is easy to miss something) you'll need to use a utility like beyond compare to compare your forum files to that of the stock files and compare differences, then you'll need to use ssh and grep to look for any suspicious edits to files and you'll need to look at recently edited/new files on the server.
