The key words are authentication, privacy, integrity, and trust. To understand computer security we have to understand the interrelationships among all of the hosts and services on our networks as well as the ways in which those hosts can be accessed. Tools that allow this kind of management are complex and usually expensive. A simple free software program that is in widespread use whose functionality is at least equal to commercial packages is cfengine. It runs on nearly every UNIX-like system and on NT with the cygwin tools installed.
Software security is about access control and software reliability.
No single tool can make computer systems secure. This was possible, even through a firewall, because the Web server on the host concerned was incorrectly configured. The bottom line is that there is no such thing as a secure operating system, firewall or not. What is required is a persistent mixture of vigilance and adaptability. Many perceive security as synonymous with network privacy or prevention of network intrusion.