A vehicle system is a vehicle system used for a vehicle, and includes: a plurality of in-vehicle apparatuses installed in the vehicle; and at least one of (i) a controller that, in accordance with a depth of penetration of a malicious attack carried out on the plurality of in-vehicle apparatuses, changes at least one of a communication method with an outside of the vehicle, a defense method against the malicious attack, or a storage method for logs pertaining to the plurality of in-vehicle apparatuses, or (ii) a determiner that determines whether or not the malicious attack is being carried out based on anomaly detection in the plurality of in-vehicle apparatuses.