An administrator implements web-filtering products but still sees that users are visiting malicious links.

Web-filtering effectiveness heavily relies on content categorization to correctly identify and block access to malicious or inappropriate websites. If users are still visiting malicious links, it is likely that the categorization database or configuration needs updating or correction.

Intrusion prevention systems (A) protect against network attacks but do not filter web content by category. Encryption (C) is unrelated to web filtering, and DNS services (D) assist with domain resolution but do not directly categorize content.

Proper configuration and maintenance of content categorization are essential to effective web filtering, as emphasized in the Security Operations domain of SY0-701【6:Chapter 12†CompTIA Security+ Study Guide】.