John Chirillo has made a career of being a "good" hacker. Good, both in the sense of knowing his craft and how to break into vulnerable systems, but also good in the sense of being one of the good guys. As a consultant, he breaks into clients networks and helps them find the holes before the "bad" hackers.

The book is intended for more intermediate to advanced users. Novices may get lost in some portions of the book that get fairly "techie". Even so, it does start off by providing a decent foundation even for those new to hacking. The first few chapters discuss the basic networking protocols and technology. By understanding how the technology is designed to work it becomes easier to understand its weaknesses or how to make it work for you.

He moves on from there to talking about the more well-known ports and the services they support (for instance standard HTTP web traffic uses port 80). He discusses the various ways a hacker can gather information necessary to build a profile of your network and the tools and techniques they can use to exploit that information to gain access.

The appendices of the book provide valuable resources that security administrators will want to keep handy on their desks: a reference of IP tables and subnetting charts; well-known ports and the services they support; a comprehensive listing of ports and services through port 1024; a listing of ports known to be used by Trojan horse and backdoor programs and which Trojans utilize them; and lastly- a detailed listing of the tools and utilities included on the CDROM.

The book is long and sometimes uses a lot of technical terms, but it provides a very comprehensive understanding of how hackers get into your networks- from gathering the information necessary to begin to scanning and finding the holes in your network to exploiting and breaking in through those holes. System administrators and Information Security professionals should definitely read this book to help them learn what they need to do to prevent these tools and techniques from working against their networks.