Winning at Candy Crush
In 2007 I did the same level of digging with a facebook puzzle solving game. Game used to post daily puzzles and top scorers (solving the puzzle in minimum time) were shown on global leaderboard. At that time, the app was not using any kind of hashing or validation. It was simply posting the score to the server so tempering the data was easier. After staying on top of global leaderboard for a few days (with impossible score of 1 second), the app developer contacted me and requested to stop cheating the system. I suggested him some changes and the game became much better