List and briefly define three classes of intruders. What are two common techniques used to protect a password file? What are three benefits that can be provided by an intrusion detection system? What is the difference between statistical anomaly detection and rule-based intrusion detection? What metrics are useful for profile-based intrusion detection? What is the difference between rule-based anomaly detection and rule-based penetration identification? What is a honeypot? What is salt in the context of UNIX password management? List and briefly define four techniques used to avoid guessable passwords.