Security Onion is a free and open source distribution of Linux. It is useful for intrusion detection, enterprise-level security monitoring, and log management. Security Onion comes with a suite of tools preinstalled, such as Snort, Suricata, Kibana, OSSEC, and many more.
Security Onion can be installed using the ISO image of Security Onion, the link for which is available on its official website. Another way to install Security Onion is to first install a standard Ubuntu 16.04 ISO image and then add the PPA and packages of Security Onion.
To download the ISO image of Security Onion, visit this link:
https://github.com/Security-Onion-Solutions/security-onion/blob/master/Verify_ISO.md.