Is it legal to hack a game?

Yes. All software issued by the makers of any publicly released game as Flight Sim X, Mortal combat etc has copyright status. Hacking violates that copyright which is a federal offense. It does not matter if the game was purchased or not. In additon whilst there may be games that can be hacked because the countrys laws are not as tight as others software houses have now found that they can seek legal steps as there was an introduction of code into their copywritten coded programme and this then breaches copywite laws as well.