I guess this question has been asked before, but I wish to have fresh answers/ideas -
Let's say there's a system which allows users to participate in a survey. Users will sign on to it using SSO (single sign on), or another way like user/password.
AND, Let's assume this system is REALLY GOOD, everybody love it and there are tons of scammers who would like to cheat by logging in more than once, stealing identities.. etc.
The big question: What would be the best method to use authenticating the users?
Possible answers, I have brought so far:
Using social security id (or any other "government" official ID number)
Phone number (less intimidating.. but also less secure)
Email + one of the above. And here's a question about emails: If I am using SSO (login with email/facebook), can I determine that the accounts entered are being actively used?
Cookies/flash/storage/... can be used in combination with another, stronger identification method, but, since log-in's are not anonymous, browser storage/cookies are not the right method anyway.
Any idea will be appreciated ! :)