A method for use in a network communication system including a plurality of electronic controllers that communicate with each other via a bus in accordance with a Controller Area Network (CAN) protocol includes determining whether or not content of a predetermined field in a transmitted frame meets a predetermined condition indicating fraud, transmitting an error frame before an end of the frame is transmitted in a case where it is determined that the frame meets the predetermined condition, recording a number of times the error frame is transmitted, for each identifier (ID) represented by content of an ID field included in a plurality of frames which has been transmitted, and providing a notification in a case where the number of times recorded for an ID exceeds a predetermined count.