With intrusion detection systems [Hat01] (IDS) the aim is to take a step forward. Once we have been able to configure our security correctly, the next step will be to detect and actively prevent intrusions.
Example 9-16. Note
IDS systems allow us to detect on time intruders using our resources or exploring our systems in search of security failures.
IDS systems create listening procedures and generate alerts when they detect suspicious situations, in other words, they look for the symptoms of potential security incidents.
We have systems based on local information, for example, gathering information from the system logs, monitoring changes in the file system or in the configurations of typical services. Other systems are based on the network and verify that there is no strange behaviour, such as spoofing, with the falsification of known addresses; controlling suspicious traffic, potential service denial attacks, detecting excessive traffic towards particular services, controlling that there are no network interfaces in promiscuous mode (a symptom of sniffers or package capturers).