A method and system for securing a controlled area network (CAN) of a vehicle is disclosed, where the CAN has a number of electronic control units (ECUs) that control vehicular systems. An on-board diagnostic port of the vehicle is monitored for suspicious activity which does not fit within the baseline profile of the destination ECU. If suspicious activity is detected, countermeasures are taken to minimize harm, such as placing the vehicle in safe mode, reducing the functionality or disabling non-critical ECUs, resetting the targeted ECU, and notifying the driver and non-targeted ECUs.