All communication over the Internet uses the Transmission Control
Protocol/Internet Protocol (TCP/IP). TCP/IP allows information to be sent
from one computer to another through a variety of intermediate computers
and separate networks before it reaches its destination.
Figure 2.2
The great flexibility of TCP/IP has led to its worldwide acceptance as the
basic Internet and intranet communications protocol. At the same time,
the fact that TCP/IP allows information to pass through intermediate
computers makes it possible for a third party to interfere with communications
as described below.
Figure 2.3
Normally, users of the many cooperating computers that make up the Internet
or other networks don't monitor or interfere with the network traffic that
continuously passes through their machines. However, many sensitive personal
and business communications over the Internet require precautions that
address the threats listed above.