What type of system is used to detect intrusions?

An Intrusion Detection System (IDS) is specifically designed to monitor network traffic or system activities for malicious activities or policy violations. The primary function of an IDS is to identify and alert administrators about potential security breaches or attacks in real-time or through periodic scanning. It analyzes traffic patterns and behaviors, looking for signatures or anomalies that may indicate an intrusion.

This system helps in maintaining the integrity, confidentiality, and availability of information by providing an extra layer of security that detects threats before they can cause harm. An IDS may not actively block or mitigate the threats but plays a crucial role in identifying them and allowing for a response.

In contrast, other options have different focuses:

An Intrusion Prevention System (IPS) not only detects but also takes proactive measures to block threats once they are identified. An Access Control System (ACS) primarily restricts user access to resources, managing permissions rather than detecting intrusions. A Network Security System (NSS) encompasses a broad array of security measures but does not singularly focus on intrusion detection, making it less specific compared to an IDS.

Understanding these distinctions reinforces the importance of the correct answer, which is established on the distinctive role that an Intrusion Detection System plays within a broader cybersecurity framework.