ON-VEHICLE NETWORK SYSTEM, FRAUD-DETECTION ELECTRONIC CONTROL UNIT, AND METHOD FOR TACKLING FRAUD

An anti-fraud method for use in an in-vehicle network system including a plurality of electronic control units that exchange data frames, each having added thereto a MAC, via a bus includes a receiving step of receiving a data frame transmitted on the bus, a verification step of generating a MAC by using data and verifying that the data frame received in the receiving step has added thereto the MAC, and an update processing step of performing an update process on the data used for generating the MAC in a case where verification has failed in the verification step.