Several users were unable to log in to Xbox Live last night thanks to a connectivity issue that prevented Xbox 360 and Xbox One users from accessing the service. Microsoft has since resolved the sign-in issue, and is now looking into other services that are affected, which include server availability issues on Xbox One. According to the Xbox Live status page:
Hi Xbox members. Are you having trouble connecting to Party Chat on Diablo III on Xbox One and Xbox 360? Additionally, Xbox One users, are you experiencing server unavailability issues? Us too, but we're working alongside our partner to get these issues fixed ASAP!
We're also aware that some of you are having trouble accessing FIFA Ultimate Team in FIFA 14. This impact is likely due to a maintenance our partner is performing at the moment. We appreciate your patience, and we'll update you as soon as we have more information on these issues.
The Xbox Live core services along with purchase and content are running without any glitches at the moment. While there isn't an official confirmation of the same, it looks like a DDoS attack that was responsible for the Xbox Live outage. Sony's PlayStation Network also went down yesterday, with hacker group Lizard Squad taking credit for both outages.
Is anyone having issues with the Xbox Live Login servers?— Lizard Squad (@LizardSquad) August 24, 2014
Thanks Kyle for the heads up!