A SECURITY MODULE FOR A CAN NODE

A security module (460) for a CAN node (402). The security module (460) comprises: a RXD input interface for receiving data from a CAN bus (404), and a TXD output interface for transmitting data to the CAN bus (404). The security module (460) is configured to: receive a CAN frame from the CAN bus via the RXD input interface; compare an identifier of the received CAN frame with at least one identifier associated with a local controller (410); and upon detection of a match between the identifier of the received CAN frame and the at least one identifier associated with the local controller (410), output an error signal to the CAN bus via the TXD output interface by setting a predetermined plurality of consecutive bits (682) in the CAN frame to a dominant value. The predetermined plurality of consecutive bits (682) identifies a security error to CAN nodes connected to the CAN bus (404) and is at least 10 consecutive bits.