Chapter 15 Security Profiles : Web filter : Configuring Web Filter Profiles : To configure the FortiGuard Web Filter categories
  
To configure the FortiGuard Web Filter categories
1. Go to the Edit Web Filter Profile window.
2. The category groups are listed in a widget. You can expand each category group to view and configure every sub-category individually within the groups. If you change the setting of a category group, all categories within the group inherit the change.
3. Select the category groups and categories to which you want to apply an action.
To assign an action to a category left click on the category and select from the pop up menu.
4. Enable Enforce Quota to activate the quota for the selected categories and category groups.
5. Select Hours, Minutes, or Seconds and enter the number of hours, minutes, or seconds. This is the daily quota allowance for each user.
6. Select Apply or OK.
Apply the web filter profile to an identity-based security policy. All the users subject to that policy are restricted by the quotas.
 
If you look at your logs carefully, you may notice that not every URL connection in the log shows a category. They are left blank. If you take one of those URL and enter it in the FortiGuard website designed to show the category for a URL it will successfully categorize it.
The reason for this is that to optimize speed throughput and reduce the load on the FortiGuard servers the FortiGate does not determine a category rating on scripts and css files.