Last night, Xbox Live was down for about an hour, reportedly due to a denial of service attack. A group calling itself the Lizard Squad has taken responsibility, taking to Twitter first to note
Xbox Live #offline
— Lizard Squad (@LizardPatrol) December 2, 2014
and then to promise
That's a small dose of what's to come on Christmas. #LizardSquad
— Lizard Squad (@LizardPatrol) December 2, 2014
The Xbox Live status page showed a number of problems overnight, but now shows that all systems are up and running. Microsoft has not yet commented on the apparent outages, and so there's no real indication that the outages were a result of an attack, other than the claims of the Lizard Squad Twitter account. The group has previously claimed responsibility for other attacks, including bringing down the PlayStation Network, League of Legends, and World of Warcraft earlier this year.
In addition, a number of fake Xbox Support Twitter pages have appeared overnight, some offering giveaway Xbox systems "as a apology for the upset". Remember that the official Xbox Support Twitter accounts are all verified.