Greet's AOer's. I was searching google for some research into Advanced Security of Linux/Unix system's as I wanna help to secure my OpenBSD system. As I was searching, I came across this interesting e-book so to speak (it's kinda in notecard form too, oddly enough) that goes deeply into many topic's involving *nix security. I think it's a must read for the *nix Admin/User and it cover's topic's ranging from HoneyPot's, Network Design's, Installation Security, Defense-In-Depth, Workstation's and Server's, and it even goes into some tool's used for security of *nix system's. Enjoy!

P.S: It is a bit out-dated, but still has plenty of information that is useful.