prevent posting if post contains certain words

[jb605]

I am wondering if there exists such a hack:

If the post submitted contains certian words, simply does not allow it to be posted. Either return to the forum index as if it has succeed (try to full the user who tries to post censored words) or give some sort of error.

Is there such a hack? Or can somebody shed some light on how should I implement it myself if it does not exist?

Thanks