INTRODUCTION

The offense seems to be getting the upper hand. Rarely a day goes by without news of a new exploit for a software vulnerability, a more effective method of distributing spam (my inbox can attest to this), or a high-profile theft of sensitive personal data from a corporation or government agency. Achieving secure computing is a perpetual challenge. There is no shortage of technologies designed to foil crafty black hats, and yet they continue to successfully compromise systems and networks.

For every class of security problem, there is almost certainly either an open source or proprietary solution designed to combat it. This is particularly true in the areas of network intrusion detection systems and network access control devices—firewalls, ...

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