This OS fingerprinting probe checks the initial TCP Window size. TCP
						stacks limit the range of sequence numbers allowable within a session to
						maintain the "connected" state within TCP protocol logic. The initial window
						size specifies a range of acceptable sequence numbers that will qualify as a
						response to an ACK packet within a session. Various operating systems use
						different Initial window sizes. The initial window size can be sampled by
						establishing an ordinary TCP connection.