Abstract: An information processing device according to the present invention is communicably connected on a network and is capable of executing online a competitive type electronic game with a game opponent, and is provided with: storage means for storing a program for the competitive type electronic game, operation means for operation by an operator, calculation means, and image generation means. The calculation means calculates a forecasted future position of an operation target object in a game space in response to operation by the operator, then packetizes information thereof and sends this via the network to an opponent terminal and also receives packets sent from the opponent terminal. When an omission or delay has occurred in reception of the packet, the image generation means generates a game image including an opponent object using the forecasted future position contained in a packet that has been received prior to a current reception.

Abstract: In an online game irregularity detection method conducted in an online game system in that a plurality of clients are connected to a game server through a network, a play log showing an execution state of an online game is acquired from a client being a verification target in the plurality of clients, and the play log is verified by reproducing an execution of the online game based on the play log being acquired. Accordingly, it is determined that an illegal act occurs when a first result value shown by the play log is not identical to a second result value obtained by reproducing the execution of the online game as a result from comparing the first result value with the second result value.