Anomaly detection device, anomaly detection method, and recording medium

An electronic control unit in an in-vehicle network included in a vehicle, the in-vehicle network including the electronic control unit, a plurality of other electronic control units (ECUs) and a network, the electronic control unit comprising:

• a vehicle control processor that performs processes relating to vehicle control;
• a communication circuit;
• a processor;
• and
• at least one memory including at least one set of instructions that, when executed by the processor, causes the processor to perform operations including:
• obtaining a message from the vehicle control processor and transmitting the message to the network using the communication circuit, and receiving a message from the network using the communication circuit and notifying the message to the vehicle control processor;
• holding, in the at least one memory, a received ID list which is a list of IDs of messages from the plurality of other ECUs received from the network by the communication circuit and notified to the vehicle control processor;
• in the case where an ID of the message from one of the plurality of other ECUs that is received by the communication circuit from the network is not included in the received ID list, adding the ID to the received ID list;
• and
• in the case where an ID of the message obtained from the vehicle control processor is included in the received ID list, causing the communication circuit not to transmit the message to the network.