Explanation:
Different services use different ports. When a service is enabled on a computer, a network port is opened for that service. For example, enabling the HTTP service on a web server will open port 80 on the server. By determining which ports are open on a remote server, we can determine which services are running on that server. A port scanner is a software application designed to probe a server or host for open ports. This is often used by administrators to verify security policies of their networks and by attackers to identify running services on a host with the view to compromise it. A port scan or portscan can be defined as a process that sends client requests to a range of server port addresses on a host, with the goal of finding an active port. While not a nefarious process in and of itself, it is one used by hackers to probe target machine services with the aim of exploiting a known vulnerability of that service. However the majority of uses of a port scan are not attacks and are simple probes to determine services available on a remote machine.