Expertise, for performing classification of a type of network traffic, can be encapsulated in a module. A set of modules, as currently available to a traffic controller, can be referred to as a collection. Programming language constructs are introduced that facilitate the writing of modules customized to identify network traffic that is peculiar to a particular user, or to a relatively small group of users. An example programming language, based on Tcl, is introduced. A key aspect is event-driven programming, and the “when” command construct is introduced. Three important event types, that can trigger a “when” command, are CLIENT_DATA, SERVER_DATA, and RULE_INIT. Another key aspect is an ability to keep state information between events. Constructs for intra-session, intra-module, and global state are introduced. A module can be blocked from executing more than once for a session. Successful execution of a module can be specified by a “match” statement.