To filter websites based on their reputation using GFI WebMonitor go to Manage and then click Policies. Select the policy you would like to change from your policy list, and click Edit. Go to the Websites section and select Remove All. You can then set the reputation filter from one to five, one being the best reputation and five being the worst reputation. Once the selection has been made simply click Save.

How to enable reputation blocking in GFI WebMonitor