CompTIA Network+

Answer: A - A port scanner searches a system for ports that are open.
Key Takeaway: A port scanner searches a host, which is usually a server, for open ports. Portscans are run by both security personnel and attackers. Security personnel, such as network administrators and consultants, use them to see what ports the equipment is listening on to harden them by shutting down nonessential ports. Attackers obviously use them to see which ports are open so they can compromise them.