Stephen Northcutt and his coauthors note in the superb Intrusion Signatures and Analysis that there's really no such thing as an attack that's never been seen before. The book documents scores of attacks on systems of all kinds, showing exactly what security administrators should look for in their logs and commenting on attackers' every significant command. This is largely a taxonomy of hacker strategies and the tools used to implement them. As such, it's an essential tool for people who want to take a scientific, targeted approach to defending information systems. It's also a great resource for security experts who want to earn their Certified Intrusion Analyst ratings from the Global Incident Analysis Center (GIAC)--it's organized, in part, around that objective.

The book typically introduces an attack strategy with a real-life trace--usually attributed to a real administrator--from TCPdump, Snort, or some sort of firewall (the trace's source is always indicated). The trace indicates what is happening (i.e., what weakness the attacker is trying to exploit) and the severity of the attack (using a standard metric that takes into account the value of the target, the attack's potential to do damage, and the defenses arrayed against the attack). The attack documentation concludes with recommendations on how defenses could have been made stronger. These pages are great opportunities to learn how to read traces and take steps to strengthen your systems' defenses.

The book admirably argues that security administrators should take some responsibility for the greater good of the Internet by, for example, using egress filtering to prevent people inside their networks from spoofing their source address (thus defending other networks from their own users' malice). The authors (and the community of white-hat security specialists that they represent) have done and continue to do a valuable service to all Internet users. Supplement this book with Northcutt's excellent Network Intrusion Detection, which takes a more general approach to log analysis and is less focused on specific attack signatures. --David Wall

Topics covered:

• External attacks on networks and hosts, as they appear to administrators and detection systems monitoring log files
• How to read log files generally
• How to report attacks and interact with the global community of good-guy security specialists
• The most commonplace critical security weaknesses
• Traces that document reconnaissance probes
• Denial-of-service attacks
• Trojans
• Overflow attacks
• Other black-hat strategies