OSSEC is an open source project started by Daniel Cid and was made public back in 2004. In 2009 Trend Micro acquired the OSSEC project keeping it open source and free.
OSSEC is a scalable, multi-platform, open source Host-based Intrusion Detection System (HIDS). It has a powerful correlation and analysis engine, integrating log analysis, file integrity checking, Windows registry monitoring, centralized policy enforcement, rootkit detection, real-time alerting and active response. It runs on most operating systems, including Linux, OpenBSD, FreeBSD, MacOS, Solaris and Windows.
Visit OSSEC project website >>