XRAY

Many people tend to think that they are not a interesting target for Attackers, but thats where they are wrong. End-User systems are perfect for an Attacker to hide his trail and launch attacks from your System so he cant be traced back.

A Firewall offten doesn't help against Attacks and it doesnt show you when an unknown attack is launched against your system if its directed at an port that is allowed to be accessed from the outside on the Firewall. Thats where the IDS comes into play.

It analyzes EVERY packet that your System receives over the LAN or WAN and if it detects suspicious behaviour, it will notify the Administrator and log the Data for future investigation.

Not only Attackers are a problem, but also automated software, Viruses and Worms which scan the internet for vulnerable Hosts to infect by first launching an Exploit against all Systems they find and then install backdoors on the compromised system and your host will start scanning itself for new targets.

Also a big problem for the computer industry are so called 0day Exploits which are bugs not known to the public and therefore noone can patch properly against such attacks. With Xray's detection mechanisms it is possible to even spot some 0day exploits since it doesnt only look for specific patterns but also suspicious data that is contained in most exploit codes.

You want to be really secure? Then you need an IDS! Only a Firewall wont help much against attacks.