My sole account got FIFA'd while I was away on vacation - I logged in after two weeks away from home and got the "your account was last logged in on another console" pop-up. :/ After some digging on Xbox.com through my account history, I found about 1000 points spent on FIFA packs and 3 new achievements on FIFA, a game that I don't even own. Luckily, I was paranoid enough to remove my CC info when the PSN hack happened, and I've used prepaid cards for my Live sub for years.
I contacted MS support on the phone, told them the whole story (and that I was familiar with FIFA account hacks), and they were surprisingly responsive. My account was never taken offline, but they did force another account redownload even though I'd already done that, and they issued me a code for 1000 points, all within 24 hours.
I have no concept of how secure my account is now (admittedly, I did have a really simple password on it), but hey, Internet tough guy, you just bought me 35 free Gamerscore points!
It also justifies my refusal to tie my CC to any of my consoles.