Security is a big issue these days, and everywhere you turn there are more references to security, more focus on security, and more companies making a buck off of your security (or lack thereof). The linsec.ca online book is meant to be a collaborative work by the community for the community, detailing various aspects of security. There are numerous sites dedicated to security for a particular operating system, ie. sites that are devoted to Linux security, or FreeBSD security, etc. but there are few sites that will take a step-by-step primer to all operating systems for security. This site aims to be one of those few in that it is not specific to any one operating system, but instead covers many different operating systems. Of course, they all have a common base in that they are operating systems based on or styled after a flavor of UNIX, whether it be Linux (and it's many distributions), BSD (and it's many derivitives), or UNIX proper. Speaking on a personal note, I use Linux and Mac OS X daily, so those are the two systems I will attempt to cover in-depth. The purpose of using a wiki as the "content management" of this site is to allow others who are more knowledgeable in systems such as FreeBSD or OpenBSD, to make their contributions.
A lot of areas will overlap; common-sense and some of the "basics" will apply to any operating system you use. Some areas, like specific tools, file system considerations, and firewall code, may be specific to one or more operating systems, but likely will not apply to others. In this, we hope to give a good "spread" over the various "*NIX-ish" operating systems out there.
On a final note, the site may seem to be in a state of flux at times, and some parts may have spelling errors or grammatical errors. This is because the site is being written and edited "live". Please forgive some mistakes; often I will write a few pieces and then go back and edit them afterwards.