FRAUD DETECTION METHOD AND FRAUD DETECTION ELECTRONIC CONTROL UNIT

A misuse detection electronic control unit in a vehicle network system including a plurality of electronic control units that communicate with one another through buses in accordance with a CAN protocol includes a transceiver unit that performs a step of receiving a data frame transmitted through the buses and a misuse detection process unit that performs a detection step of performing, as misuse detection for a target data frame, which is a data frame having a first identifier, evaluation in accordance with a reception timing of a reference data frame, which is a data frame having a second identifier different from the first identifier, and a reception timing of the target data frame on the basis of a certain rule specifying a reception interval between the reference data frame and the target data frame. The detection step includes an evaluation of the likelihood that the target data frame is unauthorised.