If you're really worried then put in some security measures like checking the file size or something. If any one of your files has been messed with, don't run the game.
Personally, I wouldn't be too concerned about it. If they break the game, they can't play it, and they have no one to blame but themselves. If they mod the game... well, no biggie. Put in a static title screen that will always show you were the original creator no matter what. It's not like people can claim they made the game then.
And even if people are modding your game, that means that they're so interested in it that they want to extend the life of your game. It should be taken as a compliment.
Hell, you could even be nice about it and show people how to mod your game. If you want. It's all a matter of perspective