This part of the book is about the ways in which individual UNIX computers communicate with one another and with the outside world, and the ways that these systems can be subverted by attackers to break into your computer system. Because many attacks come from the outside, this chapter is vital reading for anyone whose computer has outside connections.

• Chapter 14, Telephone Security, describes how modems work and provides step-by-step instructions for testing your computer's modems to see if they harbor potential security problems.

• Chapter 15, UUCP, is about the UNIX-to-UNIX copy system, which can use standard phone lines to copy files, transfer electronic mail, and exchange news. This chapter explains how UUCP works and tells you how to make sure that it can't be subverted to damage your system.

• Chapter 16, TCP/IP Networks, provides background on how TCP/IP networking programs work and describes the security problems they pose.

• Chapter 17, TCP/IP Services, discusses the common IP network services found on UNIX systems, coupled with common problems and pitfalls.

• Chapter 18, WWW Security, describes some of the issues involved in running a WWW server without opening your system to security problems. The issues discussed here should also be borne in mind when operating any other kind of network-based information server.

• Chapter 19, RPC, NIS, NIS+, and Kerberos, discusses a variety of network information services. It covers some of how they work, and common pitfalls.

• Chapter 20, NFS, describes how Sun Microsystems' Network Filesystem works and its potential security problems.