Chapter 15 Unified Threat Management for FortiOS 5.0 : Web filter : Web Site Filter : Web Site Filter actions : Monitor
  
Monitor
Traffic to, and reply traffic from, sites matching a URL pattern with a monitor be allowed through in the same way as the “Allow” action. The difference with the Monitor action being that a log message will be generated each time a matching traffic session is established. The requests will also be subject to all other Security Profiles inspections that would normally be applied to the traffic.