When I went to my local bank of america to file a claim and get a new card the guy there said this happens all the time with Xbox Live users. They bought From Dust, Vanquish someone warhammer arcade game and something else. Someone used my debit card to buy $75 worth of Microsoft Zune points and spent all the points on my xbox.
And it seems the problem isn't limited to Live but also to Games for Windows accounts too.
There's a 5 page thread at Neogaf with people describing their troubles and then their subsequent lengthy experiences with xbox live support. I have a couple friends who've had their accounts hacked and credit cards charged for over a hundred dollars each.
