We've got integrity checking on all calls back to our server (eg. when unlocking achievements and buying items).

We can also ping a game developer provided secure callback URL to let them know when we have seen a purchase or an achievement.

It _is_ possible to hack the flash content while it is running to unlock the achievements etc on the client, but the vast majority of players (99.9%) don't do this, because: a) it defeats the purpose of playing the game b) it is hard

So in reality it isn't a problem for game developers or for us :)