How to defend against users with Multiple Accounts?

Question

We have a service where we literally give away free money.

Naturally said service is ripe for abuse. To defend against this we do the following:

• log

Answer 1

I think only way is to bind your users accounts to 'real world' information, like his/her passport number, for instance. Of course, you'll need to make sure that information is securely stored and to find some way to validate it.