What are the services running on the target machine?

Now you are familiar with how to scan the IP address and identify a live host within a subnet. In this section, we will discuss the services that are running on a host. These services are the ones that are using a network connection. The service using a network connection must open a port; from a port number, we can identify which service is running on the target machine. In pentesting, the significance of port scanning is to check whether any illegitimate service is running on the host machine.

Consider a situation where users normally use their computer to download a game, and a Trojan is identified during the installation of the game. The Trojan goes into hidden mode and opens a port and sends all the keystrokes log information to the hacker. In this situation, port scanning helps to identify the unknown services that are running on the victim's computer.

Port numbers range from 0 to 65536.The well-known ports (also known as system...