Which of the following best describes host-based intrusion detection systems (HIDS)?

Host-based intrusion detection systems (HIDS) are specifically designed to monitor and analyze the activities of individual computers or devices within a network. By being installed directly on these devices, HIDS can effectively track changes in system files, detect suspicious behavior, and provide alerts about potential security threats that may originate from inside the host itself. This localized approach allows HIDS to gain detailed insights into user activity, system log files, and application behavior, which network-based systems might overlook.

In contrast, monitoring network traffic pertains to network-based intrusion detection systems (NIDS), which focus on traffic flowing across a network rather than on individual hosts. Preventing unauthorized access to network routers involves security measures that are not directly related to the function of HIDS. Similarly, the role of HIDS does not involve data encryption; rather, it is about detecting and responding to potential intrusions on a per-device basis. Understanding these fundamental functions of HIDS clarifies why the option that states they are installed on individual computers or devices is the most accurate.