Microsoft is currently dealing with some high-profile hackings that have compromised the Xbox Live accounts of former and current Microsoft employees. The attack apparently used a series of stringed social engineering tactics that collected social security numbers and other information necessary to gain access to the accounts.
A group of attackers are using several stringed social engineering techniques to compromise the accounts of a handful of high-profile Xbox Live accounts held by current and former Microsoft employees. We are actively working with law enforcement and other affected companies to disable this current method of attack and prevent its further use.
It's not clear what Microsoft will be able to do to prevent this from happening in the future. Microsoft needs a way to properly identify an account's owner, but they can't prevent third-parties from giving out that private information.