A security system includes a proxy site that interconnects a protected site and one or more responder sites using a computer network. The protected site operates an event data collector coupled to sensors that when activated, produce event data. The event data collector can initiate connections with an event processor in the proxy site to transmit the event data to the proxy site for access by one or more of the responder sites. The event processor can receive and store the event data and can provide notifications to the responder sites of the stored event data. The responder sites can periodically poll the proxy site and can receive responses that reference available event data associated with those responder sites. The system allows responder sites share references to event data, and allows the event processor to use event rules to notify different responder sites in different manners according to different event types.