Xbox 360 hackers have found an exploit that has cost Microsoft $1.2 million.
The users calculated an algorithm that allows them to re-use previously redeemed codes and stockpile Microsoft Points, according to Save and Quit.
The method could be used over and over again, giving hackers 160MSP each time. One Xbox 360 owner claimed to have generated $150 points in just 20 minutes.
Microsoft has since found a way to block people from using this exploit, but has been unable to identify the hackers.