Report to game.elements@gmail.com
Bear in mind, though, that a lot of 'hacks' can be explained by desync or mutation, and although I'm not zanz, loads of emails that say 'FrankThePigeion is a hacker! Ban him!' would probably get a bit annoying.
And Chival, calm down - it is only a game. Although you are right, mud sticks, and all that.