Which system actively takes preventative actions against unacceptable activities?

An Intrusion Prevention System (IPS) is specifically designed to actively monitor network traffic and detect potential security threats. What sets it apart is its capability to not only identify but also to take immediate action against suspicious activities that could compromise network integrity. This means that when a threat is detected, an IPS can automatically block or prevent the harmful activity from occurring, thus providing real-time protection.

This proactive approach is vital for maintaining network security, especially in environments where the stakes are high and timely responses can prevent data breaches or other malicious activities. By being able to react to threats as they emerge, an IPS plays a critical role in a robust cybersecurity strategy.

In contrast, an Intrusion Detection System (IDS) is primarily focused on monitoring and alerting about potential threats, but it does not intervene or take preventive measures. A Proxy Server primarily serves as an intermediary for requests from clients seeking resources from other servers, offering functionalities such as caching and content filtering, rather than directly preventing intrusions. A Circuit-Level Gateway operates at the transport layer to control network access but lacks the capabilities of actively preventing unauthorized activities in real time like an IPS.