Hackers were able to steal approximately $1.2m from Microsoft due to an exploit on Xbox Live, which allowed them to re-use old costs and stockpile Microsoft Points.
The hackers generated an algorithm which exploited the bug that allowed them to re-use 160MSP codes. Some hackers are reported to have generated over $150 in 20 minutes.
Microsoft has since blocked the algorithm, but they have been unable to find out who actually exploited it in order to get free points on their service.
Source: Save and Quit