I am half way through writing an online game which I would like to make open source so that others can build upon what I have done and add new features. The problem is that the game is an adaption of a turn based board game using dice, and if people can modify the source code and build their own version they can use this to cheat by modifying the game to always make favourable dice rolls.

Can anyone suggest ways to tackle this?

The online game uses a client server architecture, I though of moving all the dice rolls to the server but for performance reasons its much better done on the client.

Is it possible to somehow verify the version of all the class files to ensure they haven't been modified when playing on the server??

Ideas, thoughts, comments welcome!