Prevent users from starting multiple accounts?

Question

I know that in the end it, can\'t be done.

But, what are the options to:

  a) limit the options for persons to create multiple accounts,
  b)

Answer 1

I think the best method would be to remove the incentives for creating multiple accounts.

Do you limit the users in any way? Can those limits be overcome (easily) by creating multiple accounts? If so, then maybe you should think about removing those limits.

Answer 2

One common option is to verify the persons identity through their e-mail. Actually make them respond to an e-mail sent to their account. Some sites take this a step further and don't allow addresses from domains such as yahoo, g-mail, hotmail, etc ...

Answer 3

You could send users a SMS message to verify before creating the account. Since people can't get cell phone numbers as easily as they can get email addresses, this might work. Some people might be able to get two or three accounts, but not an unlimited number. There are a number of services that let you send SMS messages programmaticly, including Gizmo SMS, Text4Free and TxtDrop.

Of course, this requires users to have cell phones, and be willing to provide you with the number.

Answer 4

Ask users to register with a credit card. You don't have to charge anything to the card, you can just check that the card is valid.

Answer 5

I think an alternative direction to take with this is to let the "big boys" do it.

http://oauth.net/

Offload the authentication of your site to a well-known 3rd party like Google or Facebook. It won't prevent duplicate accounts, but it's nice to think that the latest in spam prevention and whatnot is automatically implemented for you.

Answer 6

You can't and you shouldn't. You are not dealing with the real world guys, but with accounts, so treat them as abstract entities which have the equal rights to live.

Some options I can imagine on the fly:

-- Only one account for email address. But I can create more then one email... or use Mailinator.

-- Long and tedious verification procedure. But that will discourage the users from registration

-- bind the IP to the account and block(temporarily?) that IP from creation of another account. But two different users with the same gateway will be blocked...

-- Use the cookies. But the user can delete them.