An Intrusion Prevention System (IPS) actively blocks malicious traffic, such as code execution or injection attacks, by matching against known signatures or anomalies, protecting the webserver until patches are applied. Intrusion Detection System (IDS) only detects and alerts, not blocks. Anti-virus and anti-rootkit are less effective for web-based attacks. The original document's answer B is incorrect, as IDS does not prevent attacks. Exact extract: "IPS provides active protection by blocking malicious traffic based on signatures or anomaly detection... Unlike IDS, which only detects and alerts, IPS can drop packets to prevent attacks like code execution or SQL injection."