In recent years, the network attack become more and more widespread and difficult in against. The traditional technique, such as Firewall is good, but when malicious traffic originates from inside network or enters through a hole in the firewall you may need another line of defense to protect you. This is a article introducing the concepts of IDS, what they do, the functions they serve, the classification of IDS, how you might use an IDS to monitor for and detect suspicious or malicious activity on the network and the di...