Prelude is an Hybrid IDS framework, that is, it is a product that enable all available security application, be it opensource or proprietary, to report to a centralized system. In order to achieve this task, Prelude relies on the IDMEF (Intrusion Detection Message Exchange Format) IETF standard, that enables different kinds of sensors to generate events using an unified language.
Prelude benefits from its ability to find traces of malicious activity from different sensors (Snort, honeyd, Nessus Vulnerability Scanner, Samhain, over 30 types of systems logs, and many others) in order to better verify an attack and in the end to perform automatic correlation between the various events.