An attacker uses a combination of techniques to determine the state of the
						ports on a remote target. Any service or application available for TCP or
						UDP networking will have a port open for communications over the network.
						Although common services have assigned port numbers, services and
						applications can run on arbitrary ports. Additionally, port scanning is
						complicated by the potential for any machine to have up to 65535 possible
						UDP or TCP services. The goal of port scanning is often broader than
						identifying open ports, but also give the attacker information concerning
						the firewall configuration. Depending upon the method of scanning that is
						used, the process can be stealthy or more obtrusive, the latter being more
						easily detectable due to the volume of packets involved, anomalous packet
						traits, or system logging. Typical port scanning activity involves sending
						probes to a range of ports and observing the responses. There are four types
						of port status that a port scan usually attempts to discover:1. Open Port: The port is open and a firewall does not block access to
							the port2. Closed Port: The port is closed (i.e. no service resides there) and
							a firewall does not block access to the port3. Filtered Port: A firewall or ACL rule is blocking access to the
							port in some manner, although the presence of a listening service on the
							port cannot be verified4. Unfiltered Port: A firewall or ACL rule is not blocking access to
							the port, although the presence of a listening service on the port
							cannot be verified.