Guest Editor's Introduction: Unwanted Traffic: Finding and Defending against Denial of Service, Spam, and Other Internet Flotsam

When the Internet's precursors began - as research projects in the US government and academia - they were small, cooperative networks that looked toward a broader goal of a robust, worldwide network in which the constituent parts worked together for the benefit of the whole. One university might send its data packets through another to get them to a third. Domains would be offline for significant periods. Servers would use dial-up modems to connect briefly to see if there was any work for them to process. Because of this background, network protocols, from the lower layers up to the application layer, were designed with fairly little protection. Consequently, spoofing of everything from IP addresses to email addresses is now possible. Packets can be inserted to fool name resolution (domain name system) requests. Passwords can be intercepted en route. Excessive data volume can overwhelm a server or an entire network. Many protocols started life with no authentication mechanisms in them and lacked any provisions for checking the legitimacy of either side of the transaction.