1. A method for detecting unique users for advertisement or content targeting, the method comprising: at a bid management system, receiving a bid request with initial fingerprint context data for a user and for content that is requested by such user, wherein the bid request is received with or without a user identifier; at the bid management system, determining an optimum bid for the bid request based on the initial fingerprint context data for the user and the content; from the bid management system, sending the optimum bid with a reference to an advertisement and a script for obtaining additional fingerprint context data from a device of the user; and at the bid management system or a unique user detection system associated with such bid management system, receiving the additional fingerprint context data and assigning a unique user identifier in association with a combination of the initial and additional fingerprint context data.