public static function anonymousId()
    {
        if ( self::$anonymousId === null )
        {
            $ini = eZINI::instance();
            self::$anonymousId = (int)$ini->variable( 'UserSettings', 'AnonymousUserID' );
            $GLOBALS['eZUserBuiltins'] = array( self::$anonymousId );
        }
        return self::$anonymousId;
    }