A security apparatus includes a receiver that receives a frame front at least one network, a parameter storage that stores at least one examination parameter defining a content of an examination on a frame, and processing circuitry that performs operations. The operations include judging whether a predetermined condition is satisfied for the frame received by the receiver. When the predetermined condition is satisfied, updating the stored at least one examination parameter, and when the predetermined condition is not satisfied, not updating the stored at least one examination parameter. The operations also include executing an examination, based on the stored at least one examination parameter, as to whether the frame received by the receiver is an attack frame, and performing a process depending on a result of the execution of the examination such that an influence of an attack frame on at least one electronic control unit is suppressed.