The case studies, large and small, are the best part of this book. Northcutt opens with a technical brief on the methods used by Kevin Mitnick in his attack upon Tsutomu Shimomura's server. In documenting that famous attack, Northcutt explains SYN flooding and TCP hijacking with clarity and detail: readers get a precise picture of what Mitnick did and how Shimomura's machine reacted. A former security expert for the U.S. Department of Defense, Northcutt explains how a system administrator would detect and defeat an attack like Mitnick's. Another case study appears later in the book, this one in the form of a line-by-line analysis of a .history file that shows how a bad guy with root privileges attacked a Domain Name System (DNS) server. Reading Northcutt's analysis is like reading a play-by-play account of a football match. Network Intrusion Detection is one of the most readable technical books around. --David Wall