A method and system for detecting intrusion on a CAN bus or vehicle network and neutralizing unauthorized intrusions. The system monitors the bit timing characteristics of CAN bus messages, message establishes trusted bit timing characteristics, and identifies unauthorized CAN bus messages. The device neutralizes unauthorized messages on the CAN bus by injecting data on the CAN bus at the appropriate time, preventing the unauthorized messages from being received, and presents alerts upon detection of the one or more of intrusions. It can be used as a standalone or hard-wired system, and may be accessible to the ODB-II port, relay or fuse port on a vehicle and may put other electronic control units on the vehicle into a safe operating mode upon receipt of the intrusion, neutralize all CAN message identifiers or set the intrusion detection flag to TRUE for all CAN message identifiers, sent by the same electronic control unit node.