Deep packet inspection is the heart of a new type of filter called intrusion prevention systems (IPS), which are designed to identify and drop packets that are part of an attack. IPSs use several techniques to identify undesirable packets. One involves checking packet contents against a database of patterns (signatures) of known attack methods. Another involves developing a profile of “normal” traffic and using statistical analysis to identify packets that do not fit that profile. Most promising is the use of rule bases that specify acceptable standards for specific types of traffic and that drop all packets that do no conform to those standards. The beauty of this approach is that it blocks not only known attacks, for which signatures already exist, but also any new attacks that violate the standards.