Although various steganographic methods have been proposed that use distinct cover media, using games to hide data remains a recent development. The study presents a steganographic method based on online Tetris games, in which secret messages are embedded using a generated tetrimino sequence. Each time a person plays an online Tetris game, a new tetrimino sequence should be generated. The proposed method meets this requirement, generating a distinct stegoed tetrimino sequence for each game played. In addition, the study presents a scenario and a simulator for the proposed method. Theoretical proof and experimental results are provided to demonstrate that the proposed method is undetectable. (C) 2013 Elsevier Inc. All rights reserved.