Abstract: A method and system for targeting online advertisements. The method includes receiving a request for an advertisement from a publisher, wherein the request includes an identifying data uniquely associated with a user. The method includes sending a response to the publisher, wherein the response includes the advertisement and an image URL. The method includes receiving a request for the image identified by the image URL and a unique user cookie from the user. The method includes if the identifying data has been previously received, determining a unique user identifier associated with the user from the identifying data. The method includes if the identifying data has not been previously received, determining the unique user identifier associated with the user from the unique user cookie, and associating the identifying information with the unique user identifier.