What is Port Scanner? what is the use?

What is Port Scanner? what is the use?

Port Scanning:

Port scanning is the process of searching for active or opened ports in victim system. Just like a thief searching for gate opened house. Consider this scanning

Starting Scan.

Target Host: www.yourcompany.com or IP Address

TCP Port :7 (echo)

TCP Port :9 (discard)

TCP Port :13 (daytime)

TCP Port :19 (chargen)

TCP Port :21 (ftp)

TCP Port :23 (telnet)

TCP Port :25 (smtp)

TCP Port :37 (time)

TCP Port :53 (domain)

TCP Port :79 (finger)

TCP Port :80 (www)

TCP Port :110 (pop)

TCP Port :111 (sunrpc)

Finished.

It shows the active ports in that domain or ip address

What is the Use?

what we can do with these ports? we can communicate with the victim system remotely using those active ports. So we can get their data without their knowledge.(The thing is that you can theft their data).

Scanning for open ports is done in two ways.

Scan a single IP address for open ports:

It just like a thief who searching for any opened gate in single house.

In relation to scanning, the gate is port and house is IP address. 

We are searching for the active port in a single IP address

Eg:

searching for active ports only at 123.xx.xx.xx

Scan a range of IP address to find open ports:

Scanning a range of IP address is like thief who searching for any opened gate in a street. In relation to scanning, the gate is ports and street is range of ip address

Eg:

searching active ports only at 

123.20.xx.xx to 123.30.xx.xx