They make super secret to create a buzz but I think it works like this.
1. You buy a code from some guy for BTC.
2. You send an email to a bot that invalidates that code and sends you back two fresh ones. Thus doubling what you have.
3. You sell the new codes and get BTC.
4. Profit!
I can't believe some people can fall for that.
You'd be surprised. Sadly greed gets the better of a lot of people and blinds their judgement. Remember a fool and his money are easily parted.