As an avid player of the Sims 2, I have recently found some (rather old) news articles about a "scandal" having to do with the "nude mods" easily available for the game:
article from GameSpot,
article from About.com,
article from GamingIndustry.biz
While this was apparently right after the little circus that happened with GTA San Andreas' mini-game found through hex-editing the code, I think the issue still has some ethical implications. Do the creators of a game hold responsibility when game users hack the code to include adult situations? Should they be required to better secure their code, so that no hacking is possible? Or are the users responsible if they hack a game to have adult content?
Personally, I think that it is up to individual game owners to make sure their games don't include content they don't want in them. However, I can see some of the view point, that some games are made easy to change, and many people don't want games with lots of sex or violence in them available to their children. While GTA might be sold as "M for Mature" and (store) require that the buyer be 18, The Sims 2 is sold as "T for Teen", but savvy teens can easily make it into a game that would be rated "AO for Adults Only"...