A module for a vehicle includes: a first communication module that transmits and receives first data to and from a first in-vehicle module; a second communication module that transmits and receives second data to and from a second in-vehicle module; and a control module that controls relay of third data among the first communication module and the second communication module. In a case where reception data received by the control module from the first or second communication module is unauthorized, the control module stops relaying the third data in accordance with a traveling state of the vehicle satisfying a predetermined condition, The traveling state includes: the vehicle being stopped; a vehicle speed being at or below a predetermined speed; brakes being applied; a hazard indicator being on; a driver being in a state capable of driving; and/or self-driving functions being in an off state.