A network security system having a hierarchical configuration is provided. In one embodiment the present invention includes a plurality of subsystems, where each subsystem includes a plurality of distributed software agents configured to collect security events from monitor devices, and a local manager module coupled to the plurality of distributed software agents to generate correlated events by correlating the security events. Each of the subsystems can report the correlated events to a global manager module coupled to the plurality of subsystems, and the global manager module can correlate the correlated events from each manager module.