As a group, we assume that you, the reader, are at least familiar with the basics of modern TCP/IP networks and the Internet. You should know what an IP address is and what a TCP port number is, and you should have at least a rough understanding of TCP flags and the like. While we discuss security tools for a variety of operating systems, the majority of tools are used via the Unix command line, so having access to a Unix machine and knowing how to get around in a shell are necessary if you want to follow along. A few of the more advanced chapters deal with programming-related tools, so a knowledge of at least one programming language will help with these (but don't worry if you aren't a programmer, there are plenty of other chapters that don't require any programming knowledge at all). Finally, a basic knowledge of computer security is assumed. Terms such as vulnerability, exploit, and denial of service should be familiar to you if you are to truly get the most from this book.