A solution is provided to monitor Web browsing activity across an Internet based network of affiliated Web sites and to enable the Web sites to detect and to force re-authentication upon users who have had a period of network-wide inactivity longer than a site-specific maximum allowable inactivity period. The network comprises at least one network authentication server (NAS) which maintains a network-wide activity tracking (NATr) cookie. The NATr cookie comprises a set of network-wide activity tracking (NATr) parameters for each registered user. Each of the Web sites maintains a site-specific activity tracking (SATr) cookie which comprises a set of site-specific activity tracking (SATr) parameters for each registered user. The NATr parameters for each user are reset whenever the user authenticates to the network. When a user requests a page from a site, an NAS forces the user to re-authenticate when the NAS determines that the user's network-wide inactivity duration is longer than the site's maximum allowable inactivity period.