LinuxSecurity.com: Packet Sniffing Overview

“A packet sniffer is a program which monitors network traffic
which passes through your computer. A packet sniffer which runs on
your PC connected to the internet using a modem, can tell you your
current IP address as well as the IP addresses of the web servers
whose sites you are visiting.

“You can watch all the un-encrypted data that travels from your
computer, onto the internet. This includes passwords and other
sensitive data that is not secured by encryption. Put a packet
sniffer on a router on the internet, and you can watch all the
network traffic that passes through that router. This includes
absolutely anyone whose data happens to pass through that
router…”

Complete
Story