A device for handling messages between a vehicle Electronic Control Unit in an ECU enclosure and a vehicle communication bus under control of a data unit, each of the messages is composed of multiple parts, the device comprising: a first physical port for connecting to the ECU; a first transceiver coupled to the first physical port for transmitting messages to, and for receiving messages from, the ECU; a second physical port for connecting to the communication bus; and a second transceiver coupled to the second physical port for transmitting messages to, and for receiving messages from, the communication bus; a message filtering unit which receives messages from said first or second transceiver and filters them according to at least one message property; the device is handling the messages under control of a data unit, and further comprising: a third physical port, being an out of band interface, for connecting to the data unit; a third transceiver coupled to the third physical port for receiving from the data unit a rule associated with a part of the message; a software and a processor for executing the software, the processor is coupled for controlling the first, second, and third transceivers; and a single enclosure for housing the first, second, and third physical ports, the first, second, and third transceivers, and the processor, wherein the single enclosure is distinct from, and external to, the ECU enclosure, wherein the device is operative to receive a message from the ECU via the first physical port, and responsive to the rule received from the data unit via the third physical port, to pass, to block, or to change and then pass, the received message to the communication bus via the second physical port, or wherein the device is operative to receive a message from the communication bus via the second physical port, and responsive to the rule received from the data unit via the third physical port, to pass, to block, or to change and then pass, the received message to the ECU via the first physical port. a first physical port for connecting to the ECU; a first transceiver coupled to the first physical port for transmitting messages to, and for receiving messages from, the ECU; a second physical port for connecting to the communication bus; and a second transceiver coupled to the second physical port for transmitting messages to, and for receiving messages from, the communication bus; a message filtering unit which receives messages from said first or second transceiver and filters them according to at least one message property; the device is handling the messages under control of a data unit, and further comprising: a third physical port, being an out of band interface, for connecting to the data unit; a third transceiver coupled to the third physical port for receiving from the data unit a rule associated with a part of the message; a software and a processor for executing the software, the processor is coupled for controlling the first, second, and third transceivers; and a single enclosure for housing the first, second, and third physical ports, the first, second, and third transceivers, and the processor, wherein the single enclosure is distinct from, and external to, the ECU enclosure, wherein the device is operative to receive a message from the ECU via the first physical port, and responsive to the rule received from the data unit via the third physical port, to pass, to block, or to change and then pass, the received message to the communication bus via the second physical port, or wherein the device is operative to receive a message from the communication bus via the second physical port, and responsive to the rule received from the data unit via the third physical port, to pass, to block, or to change and then pass, the received message to the ECU via the first physical port. a third physical port, being an out of band interface, for connecting to the data unit; a third transceiver coupled to the third physical port for receiving from the data unit a rule associated with a part of the message; a software and a processor for executing the software, the processor is coupled for controlling the first, second, and third transceivers; and a single enclosure for housing the first, second, and third physical ports, the first, second, and third transceivers, and the processor, wherein the single enclosure is distinct from, and external to, the ECU enclosure, wherein the device is operative to receive a message from the ECU via the first physical port, and responsive to the rule received from the data unit via the third physical port, to pass, to block, or to change and then pass, the received message to the communication bus via the second physical port, or wherein the device is operative to receive a message from the communication bus via the second physical port, and responsive to the rule received from the data unit via the third physical port, to pass, to block, or to change and then pass, the received message to the ECU via the first physical port.