An attacker engages in activity to detect the version or type of OS
						software in a an environment by passively monitoring communication between
						devices, nodes, or applications. Passive techniques for operating system
						detection send no actual probes to a target, but monitor network or
						client-server communication between nodes in order to identify operating
						systems based on observed behavior as compared to a database of known
						signatures or values. While passive OS fingerprinting is not usually as
						reliable as active methods it is more stealthy.