On September 1, 1997, I released a security scanner named Nmap in the fifty-first issue of Phrack magazine. My goal was to consolidate the fragmented field of special-purpose port scanners into one powerful and flexible free tool, providing a consistent interface and efficient implementation of all practical port scanning techniques. Nmap then consisted of three files (barely 2,000 lines of code) and supported only the Linux operating system. It was written for my own purposes, and released in the hope that others would find it useful.

From these humble beginnings, and through the power of open source development, Nmap grew into the world's most popular network security scanner, with millions of users worldwide. Over the years, Nmap has continued to add advanced functionality such as remote OS detection, version/service detection, and the Nmap Scripting Engine. It now supports all major Unix, Windows, and Mac OS platforms with both console and graphical interfaces. Publications including Linux Journal, Info World, LinuxQuestions.Org, and the Codetalker Digest have recognized Nmap as security tool of the year. It was even featured in nine movies, including The Matrix Reloaded, The Girl with the Dragon Tattoo, The Bourne Ultimatum, and Die Hard 4.

Nmap (Network Mapper) is a free and open source utility for network exploration and security auditing. Many systems and network administrators also find it useful for tasks such as network inventory, managing service upgrade schedules, and monitoring host or service uptime. Nmap uses raw IP packets in novel ways to determine what hosts are available on the network, what services (application name and version) those hosts are offering, what operating systems (and OS versions) they are running, what type of packet filters/firewalls are in use, and dozens of other characteristics. It was designed to rapidly scan large networks, but works fine against single hosts.

While Nmap is extremely powerful, it is also complex. More than 100 command-line options add expressiveness for networking gurus, but can confound novices. Some of its options have never even been documented. This book documents all Nmap features and, more importantly, teaches the most effective ways of using them. It has taken nearly four years to write, with constant updating as Nmap has evolved.

This book is dedicated to the Nmap community of users and developers. Your passion, ideas, patches, feature requests, flame wars, bug reports, and midnight rants have shaped Nmap into what it is today.

—Gordon “Fyodor” Lyon