Login services were knocked out earlier this afternoon.
Microsoft says a "major outage" at Xbox Live is keeping some users from logging in, and it's taking longer than expected to get the problem fixed.
As noted by The Verge, the Xbox Support account on Twitter first acknowledged that "some users have been disconnected from Xbox Live" at around 3 pm ET. Just over an hour later, the account tweeted again to say "our investigation is taking longer than expected," and advised users having trouble to keep an eye on the Xbox Status page.
The nature of the problem, and whether it's the result of a DDoS attack or some other external influence, isn't clear. The status page currently indicates that all Xbox Live features and services are up and running except for "Account and profile," which is suffering a major outage that's keeping users from logging into Xbox Live.
"You may not be able to sign-in to your Xbox profile, may be disconnected while signed in, or have other related problems," the status page says. "Features that require sign-in like most games, apps and social activity won't be available."
I tried logging in and that is indeed what happened: After entering my login details, I was dropped to a blank screen, then kicked back to the not-logged-in status page. Oddly enough, I was able to report a problem, even though I'm not logged in, something some users on Twitter said they were unable to do—so there's clearly something weird going on.
The most recent update to the status page says a "related issue" has been discovered and a resolution is pending. We'll keep an eye on things and update when the situation changes.
