An attacker uses a technique to generate an ICMP Error message (Port
						Unreachable, Destination Unreachable, Redirect, Source Quench, Time
						Exceeded, Parameter Problem) from a target and then analyze the amount of
						data returned or "Quoted" from the originating request that generated the
						ICMP error message. For this purpose "Port Unreachable" error messages are
						often used, as generating them requires the attacker to send a UDP datagram
						to a closed port on the target. The goal of this analysis to make inferences
						about the type of operating system or firmware that sent the error message
						in reply. This is useful for identifying unique characteristics of operating
						systems because the RFC-1122 expected behavior reads: "Every ICMP error
						message includes the Internet header and at least the first 8 data octets of
						the datagram that triggered the error; more than 8 octets MAY be sent
						[...]." This contrasts with RFC-792 expected behavior, which limited the
						quoted text to 64 bits (8 octets). Given the latitude in the specification
						the resulting RFC-1122 stack implementations often respond with a high
						degree of variability in the amount of data quoted in the error message
						because "older" or "legacy" stacks may comply with the RFC-792
						specification, while other stacks may choose a longer format in accordance
						with RFC-1122. As a general rule most operating systems or firmware will
						quote the first 8 bytes of the datagram triggering the error, but some IP
						stacks will quote more than the first 8 bytes of data.