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

It's pretty difficult to generate lots of fake phone numbers that can send and receive SMS messages. SMS verification could go a long way towards cutting down on fraud. Of course, it also limits you to giving away free money to cell phone owners.