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phpsecurityuser-registration

Prevent multiple registrations on a survey website

Context

I am developing a survey website where anyone can vote once. Obviously I have to prevent multiple registrations for the survey to remain relevant. I force every user to login with their Google, Facebook or Twitter account. But they can authenticate 3 times if they have an account on each, or authenticate with multiple accounts on the same platform (I have 3 accounts on Google). So I thought to store their IP address, but they can still use a proxy. I could keep the HTTP User Agent with PHP's get_browser(), although they can still change browsers. I can extract the OS with a regex, to change OS is less easier than browsers. And there is also geolocation, for example with the Google Map API.

Questions

  • How to prevent multiple registrations? What kind of test can be done?
  • How to embed these tests? Execute in what order?
  • Have you already deploy this kind of solution?
Solution

  • You can verify user by mobile phone, by sending text message with some code to it. This will limit votes count to count of mobile phone numbers owned by user.