Book excerpt: Intrusion Prevention and Active Response provides an introduction to the field of Intrusion Prevention and provides detailed information on various IPS methods and technologies. Specific methods are covered in depth, including both network and host IPS and response technologies such as port deactivation, firewall/router network layer ACL modification, session sniping, outright application layer data modification, system call interception, and application shims. Corporate spending for Intrusion Prevention systems increased dramatically by 11% in the last quarter of 2004 alone Lead author, Michael Rash, is well respected in the IPS Community, having authored FWSnort, which greatly enhances the intrusion prevention capabilities of the market-leading Snort IDS