userguid.js

var guid = function() {

    var nav = window.navigator;
    var screen = window.screen;
    var guid = nav.mimeTypes.length;
    guid += nav.userAgent.replace(/\D+/g, '');
    guid += nav.plugins.length;
    guid += screen.height || '';
    guid += screen.width || '';
    guid += screen.pixelDepth || '';

    return guid;
};