PURPOSE: A network security method for using a matching relation of an ID code of a user terminal and a recording medium are provided to protect game asset in case the ID and password of a user are leaked. CONSTITUTION: An ID code of a user terminal and a recording medium are transmitted to a management server(S13). The management server includes database in which the ID code of the user terminal corresponding to the ID codes of recording mediums are matched. The management server validates a matching relation of the ID code of the user terminal from the user terminal based on database(S15). If the matching relation is verified, the management server transmits the finishing authentication signal to the user terminal(S16).
