I recommend reading Google’s post An update on our war against account hijackers. It describes the kinds of measures taken by professionally-run Identity Providers to defend against account takeover.
A message not stated but implied is that consumers and Web sites are far better off depending upon identities provided by organizations with the resources and dedication to successfully fight takeover attempts. Sites with their own username/password login systems without these defenses are vulnerable, and would be better off using federated identities from professionally-run Identity Providers.
