ABSTRACT
In computer security a very common question, is why firewall is not sufficient or how a system of detection of intruders complements to firewall. The answer is simple. While firewall only limits the entrance to the network being based on determined characteristic of the heads of the packages, the IDS go much more there, identifying the possible attacks (or attempts of intrusin) by means of the search of their signature in the head, but also in the useful data.
