Mine was h4x0r3d too, which made me ever so sad, though I only lost 960 Microsoft points since my credit card on there doesn't work.
However, I don't think Xbox is the one getting hacked. With the random and minimal damage (few people are getting this problem compared to the amount of Xbox users), I was thinking that they are getting usernames and passwords from little websites (for example, if my email for the Escapist and Xbox Live are the same) and then using the passwords they fish on the 360.
So for example, my email
[email protected] and password ilovejustinbieber get taken from fakewebsite.com. They stick that email and the password into Xbox Live, knowing that most people don't use multiple passwords. It works every so often, they smash and grab and Tippy2k2 is sad because his money went away.
Damn it! I just gave my password up, now I'm going to have to go change it again!