The general hypothesis that an Intrusion Detection System (IDS) is based on is that a security violation is associated with a pattern of system usage which can be differentiated from a normal usage pattern. An IDS is a system or device that monitors and analyzes the network traffic or system activity for any signs or indications of malicious or unauthorized actions, such as intrusions, attacks, or violations. An IDS can help to detect and alert the security incidents that may compromise the confidentiality, integrity, or availability of the network or system, as well as to provide the information and evidence of the incidents. An IDS is based on the general hypothesis that a security violation is associated with a pattern of system usage which can be differentiated from a normal usage pattern, by assuming that the behavior or activity of a legitimate or authorized user or process is different from the behavior or activity of an illegitimate or unauthorized user or process. An IDS can use various methods or techniques to differentiate the normal and abnormal patterns of system usage, such as signature-based, anomaly-based, or heuristic-based methods. Signature-based methods compare the system usage with a predefined set of rules or signatures that represent the known or expected patterns of security violations. Anomaly-based methods compare the system usage with a baseline or profile that represents the normal or expected patterns of system usage. Heuristic-based methods use artificial intelligence or machine learning algorithms to learn and adapt to the changing patterns of system usage. Used to detect known violations, used to detect a masquerader, or differentiated to detect all security violations are not the general hypotheses that an IDS is based on, as they are either too specific, too narrow, or too broad statements about the IDS. References: CISSP All-in-One Exam Guide, Eighth Edition, Chapter 6: Secure Network Architecture and Securing Network Components, page 361; CISSP Official (ISC)2 Practice Tests, Third Edition, Domain 4:
Communication and Network Security, Question 4.10, page 187.