dsniff, the tool box

a collection of tools permitting:
to audit a network,
to perform penetration testing.

two categories of tools:
to passively monitoring the network
to catch interesting data,
to facilitate the interception of network traffic
normally non-available to an attacker.

great tools to:
educate users and administrators,
obtain security budgets:
show his password and his e-mail to your boss;-)

But especially do not abuse these tools!
even if they are portable: *BSD, Linux, Solaris, Win32.