A system and method for the multi-stage analysis of incoming packets. Three stages are used, each of which addresses a particular category of threat by examining the headers and/or payload of each packet (“deep packet inspection”). The first stage detects incoming viruses or worms. The second stage detects malicious applications. The third stage detects attempts at intrusion. These three stages operate in sequence, but in alternative embodiments of the invention, they may be applied in a different order. These three stages are followed by a fourth stage that acts as a verification stage. If any of the first three stages detects a possible attack, then the packet or packets that have been flagged are routed to a central verification facility. In an embodiment of the invention, the verification facility is a server, coupled with a database. Here, suspect packets are compared to entries in the database to more comprehensively determine whether or not the packets represent an attempt to subvert the information processing system.