OSSEC (Open Source HIDS SECurity) is a comprehensive, open-source Host Intrusion Detection System (HIDS) that provides log analysis, file integrity monitoring, rootkit detection, and real-time alerting for Linux, Windows, and macOS systems.

Key Features

• File integrity monitoring (FIM)
• Log analysis and correlation
• Rootkit detection
• Active response (auto-block IP on threat)
• Centralized server and agent architecture
• Compliance reporting
• Cloud-native deployment support (AWS, Azure, GCP)

Verdict

OSSEC is the open-source gold standard for host intrusion detection on Linux servers. Its active response capabilities make it one of the few free tools capable of automatically blocking attacks in real-time.