I think I know what you're meaning. The key thing in any multiplayer game that makes it work good is the client-server relationship. It's actually a lot easier to do anti-cheat methods in multiplayer games as opposed to single player games. The key thing to remember is that the client is only INTERPRETING things from the server. The server should be doing any processing of any stats or variables, and it sends it to the client. The client only sends keystrokes and actions to the server, and then it sends it back.
Then, to take it even further, if someone was to hex edit it or something, it would only show up differently for them and not allow them to actually have any advantages or have anything in return for it.
But, then the possibility is always open for them to use a means of modifying the packet. The key to that is to encrypt most of the messages you send over to the server and client, and then have them decrypt it on return. But that's a lot more advanced, and you could setup means of figuring out if someone's doing packet editing. Anyways, hopefully in the future someone will make an encryption plugin, but from what I've heard it isn't too hard.
So it shouldn't be too easy for people to cheat, especially if you are doing a multiplayer game. As for a single player game, I'd have to agree with Deadeye, I don't really see any point to trying to protect against cheating.. All it'll do is ruin their experience.