I wasn't a fan of Hacking Exposed, largely because its Unix section was a mere 50 pages of superficial, outdated, and obvious fluff. Hacking Linux Exposed makes up for that lack by digging into Unix in much more depth.Though it is modeled after the attack/countermeasure style of the original HE, this book includes a whole chapter of security measures at the beginning that you can implement instantly to get your machine locked down before getting into the nitty-gritty detail about other things in the hacker's arsenal.I was particularly enthralled with chapter 10, which talks about what the hacker will do after they have gained root access, from simple things like adding accounts to complicated issues like kernel modules, complete with source code. Chapter 7 includes some really wonderful examples of how the hacker can abuse networking protocols themselves, something I haven't seen covered in such depth before.The book is logically organized. The first part covers the way the hackers find and probe your machine. The second talks about getting in from the outside, be it network or physical. The third part talks about gaining additional priveleges, and the last part of the book is dedicated to mail, ftp, web, and firewalls. The appendicies are actually useful. They seem to have dropped the small 1-page case studies from the original book and replaced them with longer hacker-eye-views of real attacks which are an interesting read, and really tie the book together.This book is Linux specific in it's countermeasures, but I'd recommend this to any unix user. They do a good job of discussing differences between Linux variants as well, they don't just assume everyone has a RedHat box on their desk. Very refreshing.This book is great for both the theory and practical uses. I could spend weeks implementing all the suggestions they have, but they seem to have thought of this because their risk ratings let you know where you should concentrate as you secure your systems.Like Hacking Exposed, this book also has a website, (...) but it seems more up-to-date -- for example when the ptrace bug in older kernels came out, they posted a kernel module you could compile to protect your system until you could upgrade -- and includes all the source code contained in the book.I bought two of these, one for home and one for the office, and I suggest you do the same.