For multiple hours on Saturday, the Xbox Live service was unavailable and then rumors began to spread that the service had been hacked by the Anonymous hacking group, who was being given credit for causing the outage. Later, Microsoft commented that rumors of the service being hacked were false.
Microsoft did a pretty good job letting players know there was an issue and the teams at Microsoft were hard at work addressing the issue. In the end, these things happen; and Microsoft minimized the down time and fixed the issues causing the problem.