This tutorial by finid shows us how to get OSSEC running on FreeSBD 10.1.

ossec-hidsOSSEC is an open source, host-based intrusion detection system (HIDS) that performs log analysis, integrity checking, Windows registry monitoring, rootkit detection, time-based alerting, and active response.

It’s one of the most important security applications you could install on your server and it can be used to monitor one machine or thousands in a client/server or agent/server fashion. If properly configured, OSSEC can give you a view into what’s happening on your server via email alerts to any number of configured email addresses.

This tutorial will show you how to install and configure OSSEC to monitor a DigitalOcean Droplet running FreeBSD 10.1. In addition to OSSEC’s default rulesets for user access and integrity checking, we will configure additional rules so that if a file is modified or added to the system, OSSEC will notify you by email.

Full tutorial: https://www.digitalocean.com/community/tutorials/how-to-install-and-configure-ossec-on-freebsd-10-1