At its heart, Kerio Control's Web Filter relies on a third-party service, currently provided by , to maintain a dynamic, real-time database of website categorizations. When a user requests a webpage, the firewall sends a query to this service. The service responds with the page's category (e.g., "Social Networking," "Streaming Media," "Productivity"). Based on this rating and your predefined content rules, Kerio Control either allows or denies the connection.