OSSEC markets itself as the world’s most widely used Intrusion Detection System. An Intrusion Detection System (commonly called IDS) is a software which helps us to monitor our network for anomalies, incidents or any event we determine to be reported. Intrusion Detection Systems are customizable like a firewall, they can be configured to send alarm messages upon a rule’s instruction, to apply a security measure or to automatically answer to the threat or warning as convenient for your network or device.