There was a money hack that worked by sending the amount of money multiple times to the server. It would stack up much faster on the victims client than on the server, so they would see a large amount of money but wouldn't receive anywhere near as much.
They patched this sometime in Jan 06, long time ago now. Idiotically, they came out with the same exploit for CP, which lasted quite some time before being patched.
I'm uncertain, but I think the EP hack in Eudemons, which uses the same method, is yet unpatched.