Sniffing

Capturing information that was intended for other machines on a computer network. Sniffing is one of the most popular forms of attacks used by hackers.

For example, a machine in an Ethernet network can be configured to accept all packets, no matter what destination is in the packet header. Because account and password information is often transmitted in clear-text, it is not difficult for an intruder via sniffing to compromise all the machines on the net.