A system, a method, and computer program product identify a website that is a forgery of a primary website. Client side executable code is included in a page of the primary website, which page is copied in the forged website. The client side code, when executed by a client device, determines whether the domain from which the page is served is an authorized domain. Where the serving domain is not authorized, the client device is configured to alter the execute countermeasures against the forged website, such as altering operation of the forged page.