From A to Z, this book covers Linux security. It goes into more depth than any security book I've read (and that's about twenty at last count) including the biggies like Hacking Exposed itself. The authors really took the time to research the latest-greatest tools and attacks. They included a lot of the old standards, but mostly in passing, focusing on things that are still problems, not things that are old news like so many books. No Sendmail 8.8 exploits here, and good riddance.
I'd highly recommend this book for anyone who wants to see what a hacker actually does, down to the keystrokes themselves. Most importantly, you get clear easy steps to fix the problems. When there are multiple tools that you could use, they cover them in enough depth to let you know which is best for you and your skill level.
If you want to keep others off of your machine, this is the book to buy.