I always wondered how hackers know what ports open on a system? or How they get what services running on a system? without asking the admin. Then after some Google search, I found one samurai tool called NMAP . What is NMAP? NMAP-Net work mappe r as the word suggests is a tool used to scan networks for open, closed, filtered ports, services running on a system, OS detection, or guessing!, finding some vulnerabilities. It is written by Gordon Lyon . As per my experience, it is the best handy tool, and easy to use for network scanning. In this tutorial, I’ll cover some of the Kung-Fu basics of NMAP with examples. One of the most interesting facts is that NMAP scan TypeOptionTarget . Let’s say you want to scan a host to see what the version of services running. To do this, run the following command: nmap -sV target Here TypeOptionTarget meaning is -sV which stands for scanning and V stands for version . How NMAP works as a default: When you run default command (&q