To assist a destination/intermediary node in authenticating a communications packet as originating from a certain source node, the source node hides a cryptographically generated first special value based on the packet in a header portion of the communications packet. Upon receipt of the communications packet, the destination/intermediary node cyptographically generates a second special value also based on the packet for comparison to the first special value extracted from hiding in the header portion. If the first and second special values match, the destination/intermediary node has authenticated the communications packet as originating from the source node. The foregoing may be implemented in a number of situations, but has special use in connection with the detection of packet communications vulnerability assessment probe traffic by an intrusion detection system.