A port scanner can be used to (i) attack a network and (ii) as a defense against an attack.

		this is not true because no one would like to scan their own ports.
		this is true because while a port scanner attacks the other party's network it secures the attacker's own network by removing its footprints.
		this is true because testing your own ports for vulnerabilities is defense, and checking someone else's open ports is a stage of attack.
		this is not true because a port scanner is neither a defense tool nor an attack tool. It is a document scanning software.