"Understanding Internet Protocol (IP) packets, other network
protocols, and how networks communicate bring forth both the
strengths and vulnerabilities of Internet use. Intruders such
as hackers and insiders with questionable intentions use network
scanners and packet sniffers to analyze the components of networks
in order to reveal open connections on networks, through virtual
ports, and find unguarded ports to exploit. They also employ
spoofing (masquerading as an authorized IP address to conceal their
true IP address identity) to fool a network that a message
originated from a known and trusted system."
"Protocols (rules that computers use to communicate between
systems and networks) are open, well documented and supported by a
wide variety of applications, programs, utilities and management
tools, making them both essential for network communications and
exploitable avenues for intruders. The basic structure of network
protocols must remain standard, documented and visible in order to
support software, hardware and methods to interoperate properly.
This openness required for network communication and Internet
growth also leaves network structures open to be taken advantage of
by those attempting to gain unauthorized access to data. This
includes interception of IP packets and extraction of data such as
logon user names and/or passwords within those messages."