As the creator of psad, fwknop, and fwsnort, Rash is an expert on firewalls, IDSs, OS fingerprinting, and the Snort rules language. He is co-author of the book Snort 2.1 Intrusion Detection, lead-author and technical editor of the book Intrusion Prevention and Active Response, and has written security articles for Linux Journal, SysAdmin, and;login: . Linux FirewallsSystem administrators need to stay ahead of new security