Chapter 13 Logging and Reporting : Logging and reporting overview : FortiOS features available for logging : Web Filter
  
Web Filter
Web filter logs record HTTP traffic activity. These log messages provide valuable and detailed information about this particular traffic activity on your network. Web filtering activity is important to log because it can inform you about:
what types of web sites employees are accessing
users attempting to access banned web sites and how often this occurs
network congestion due to employees accessing the Internet at the same time
web-based threats resulting from users visiting non-business-related web sites
Web Filter logs are an effective tool to help you determine if you need to update your web filtering settings within a web filter profile due to unforeseen threats or network congestion. These logs also inform you about web filtering quotas that have been configured for filtering HTTP traffic.
You must configure logging settings within the web filter profile and apply the filter to a firewall policy so that the FortiGate unit can record the activity.