Fighting against cheaters

I've no idea why it could be interesting to cheat in a single player game like my rpg Darkness Springs, but I think those cheaters might have a similar motivation as hackers of websites of free and open source projects [actually, the Irrlicht website has been hacked twice (newsarchive)].
Since the game has now a public high score list, a lot of people started to cheat themselves higher exp and gold (the list should now be clean again). Anyway, I've now built in some more agressive anti-cheating mechanisms both into the server and the client, and protected the clients code now with the just released irrfuscator 1.1 actionscript 3 obfuscator which now should it make it really difficult for those people. Bah, such a waste of development time.