Practical UNIX and Internet Security, 3rd Edition

Chapter 1. Introduction: Some Fundamental Questions

In today’s world of international networks and electronic commerce, every computer system is a potential target. Rarely does a month go by without news of some major network or organization having its computers penetrated by unknown computer criminals. These intrusions have become especially sinister in recent years: computers have been turned into attack platforms for launching massive denial of service attacks, credit-card numbers have been plundered from databases and then used for fraud or extortion, hospital medical records have been accessed by children who then used the information to play malicious practical jokes on former patients, business records have been surreptitiously altered, software has been replaced with secret “back doors” in place, and millions of passwords have been captured from unsuspecting users. There are also reports of organized crime, agents of hostile nation states, and terrorists all gaining access to government and private computer systems, using those systems for nefarious purposes.

All attacks on computer systems are potentially damaging and costly. Even if nothing is removed or altered, system administrators must often spend hours or days analyzing the penetration and possibly reloading or reconfiguring a compromised system to regain some level of confidence in the system’s integrity. As there is no way to know the motives of an intruder, and the worst must always be assumed.

People who break ...