VEHICLE-MOUNTED NETWORK SYSTEM, INVALIDITY DETECTION ELECTRONIC CONTROL UNIT, AND INVALIDITY DETECTION METHOD

A fraud sensing method for use in an in-vehicle network system including a plurality of electronic control units that communicate with each other via a bus includes a detecting step of detecting that a state of a vehicle satisfies a predetermined condition, and a switching step of switching, upon detecting that the state of the vehicle satisfies the predetermined condition, an operation mode of a fraud-sensing electronic control unit connected to the bus between a first mode in which a first type of sensing process for sensing a fraudulent message in the bus is performed and a second mode in which the first type of sensing process is not performed.