Short description of XRAY - Intrusion Detection System 1.0: A Firewall just blocks certain ports and connections, but most computers and especially servers are bound to have open ports if they are connected to the internet. This is where the IDS comes into play. It analyzes all data that arrives at your system and warns you if something suspicious is going on.
You want to be really secure? Then you need an IDS! If your System is under attack, you will know with XRAY. Try