WireShark

Description

"Wireshark is an open-source software program that is freely available to computer security investigators. It is distinguished by its ease of use and by its ability to sort out and decode hundreds of common Internet protocols that are used for different types of data communications. It is known as a sniffer, and such software programs are essential for the sleuths who track cybercriminals and spies on the Internet.

Wireshark makes it possible to watch an unencrypted Internet chat session while it is taking place, or in the case of Mr. Walton’s research in India, to watch as Internet attackers copied files from the Dalai Lama’s network." (http://www.nytimes.com/2009/05/12/science/12cyber.html?)