Enhancing user identification with privacy protection across web servers

A method of limiting sharing of visitor identity information across web sites, including:

• receiving from a visited web site server in a visitor's browser a web page that
• includes a privacy script that runs in the visitor's browser and interfaces directly or indirectly with a privacy ID server and
• includes one or more third-party apps that seek identification of the visitor;
• the privacy script running in the browser retrieving a first party cookie including a visitor ID;
• the privacy script forwarding directly or indirectly at least part of the first party cookie to the privacy ID server;
• the privacy script receiving from the privacy ID server, a site-by-app-specific ID for the visited web site and one of the third-party apps, wherein site-by-app-specific IDs for the visitor are distinct and uncorrelated among distinct pairs of the web sites and the third-party apps;
• and
• the privacy script providing respective site-by-app-specific IDs to respective third-party apps, without providing the visitor ID to the third-party apps, thereby allowing tracking of the visitor on repeat visits to the visited web site but not facilitating identification of the visitor across web sites.