Not so much hacked, as Microsoft had put a statement out saying that was the wrong term to use. Major Nelson had said the following about it:
Despite some recent reports and speculation, I want to reassure all of our 6 million Xbox Live members that we have looked into the situation and found no evidence of any compromise of the security of the Xbox Live Network or Bungie.net.”
There have been a few isolated incidents where malicious users have been attempting to draw personal information from unsuspecting users and use it to gain access to their Live account.
I also remind members of the service never to give out any personal information and refer to my link to a PDF file on how to protect your self against identity theft.