Reports of Xbox LIVE services are rolling in at such a high rate that Microsoft's Xbox Support social accounts have decided publicly assure the community that the issues are being investigated.
According to the Xbox Live Status page, core services for Xbox LIVE are currently limited. Users are reporting issues signing in and creating accounts. This appears to be the only issue users are reporting at the moment.
We're looking into troubles with sign-in currently, keep an eye here: https://t.co/99xfLMWcZW pic.twitter.com/1GuPh0GNQV
— Xbox Support (1-5) (@XboxSupport) February 16, 2016
Without being able to sign online, you won't be able to play games that require Xbox LIVE, so get ready for some single-player campaign action!