A method and system to protect users against potentially fraudulent activities associated with spoof web sites are described. According to one aspect of the present invention, the URL of a document downloaded via a web browser client is compared to the URLs in a list of URLs for known spoof sites. If the URL for the downloaded document is found in the list of URLs for known spoof sites, a security indicator is displayed to the user to indicate to the user that the downloaded document is associated with a known spoof site. According to another aspect of the invention, a security server maintains a master black list and periodically communicates updates of the master black list to the local list of a client security application.