International Journal of Computer Applications
Computer networks are usually vulnerable to attacks by any unauthorized person trying to misuse the resources. Hence they need to be protected against such attacks by Intrusion Detection Systems (IDS). The traditional prevention techniques such as user authentication, data encryption, avoidance of programming errors, and firewalls are only used as the first line of defense. But, if a password is weak and is compromised, user authentication cannot prevent unauthorized use. Similarly, firewalls are vulnerable to errors in configuration and sometimes have ambiguous/undefined security policies. They fail to protect against malicious mobile code, insider attacks and unsecured modems. Therefore, intrusion detection is required as an additional wall for protecting systems.