Abstract: An online service provides detection of tampering of game data. During game play, the service provides challenges to inspect select data in memory of a game device. A challenge includes an executable program that is configured to locate select data and analyze the select data for tampering. Upon locating the select data, the challenge computes cryptographic hash values from the located select data and returns those hash values to the online game service, where they are compared against expected hash values to determine whether data tampering has occurred on the game device. If the cryptographic hash values match, the service allows online gaming to continue. If the cryptographic hash values do not match, the service discontinues online gaming by terminating the game session for example.