An intrusion detection system (IDS) is a system used to detect unauthorized intrusions into computer systems and networks. Intrusion detection as a technology is not new, it has been used for generations to defend valuable resources. Kings, emperors, and nobles who had wealth used it in rather an interesting way. They built castles and palaces on tops of mountains and sharp cliffs with observation towers to provide them with a clear overview of the lands below where they could detect any attempted intrusion ahead of time and defend themselves.
Empires and kingdoms grew and collapsed based on how well intrusions from the enemies surrounding them, could be detected. In fact, according to the Greek legend of the Trojan Horse, the people of Crete were defeated by the Greeks because the Greeks managed to penetrate the heavily guarded gates of the city walls. Through the years, intrusion detection has been used by individuals and companies in a variety of ways including erecting ways and fences around valuable resources with sentry boxes to watch the activities surrounding the premises of the resource. Individuals have used dogs, floodlights, electronic fences, and closed circuit television and other watchful gadgets to be able to detect intrusions.