A method for a fraud detecting controller connected to networks for communication by a plurality of controllers, includes, storing fraud detection rules, determining whether a message transmitted on the network connected to the fraud detecting controller conforms to the rules, receiving data including updated fraud detection rules and network type information indicating one network type to which the updated fraud detection rules are to be applied; and determining whether a vehicle having an on-board network is running, the on-board network including the plurality of controllers. When the vehicle is running, additionally determining whether the network type information indicates a drive network which is connected to a controller related to vehicle travel, when the network type information indicates the drive network, not updating to the updated fraud detection rules, and when the network type information does not indicate the drive network, updating to the updated fraud detection rules.