A security device connected to at least one bus in a vehicle is provided. The security device determines, with regard to a frame received from the at least one bus, whether predetermined conditions are satisfied to determine whether the frame is a suspect of being an attack frame. The security device transmits, a determination request to an external device outside of the vehicle in a case where the predetermined conditions are satisfied, and obtains determination results from the external device in accordance with the determination request. The security device outputs first presentation information in the case where the predetermined conditions are satisfied, and outputs second presentation information in a case where the determination results are obtained from the external device.