"User Impact: Users may have been unable to log in to Office 365 services.
Final status: We monitored the service and worked with some affected customers to confirm restoration. In some cases, affected users may need to restart their browser or application in order for sign-in to begin functioning properly.
Scope of impact: Customer reports indicated that many users likely experienced impact related to this event. Our analysis indicated that this issue could have potentially affected any of your users intermittently if they were routed through the affected infrastructure.
Start time: Wednesday, May 10, 2017, at 7:32 PM UTC
End time: Wednesday, May 10, 2017, at 8:12 PM UTC
Preliminary root cause: A recent change introduced a configuration issue that caused authentication for Office 365 services to become degraded.
- We're reviewing our monitoring services to find ways to reduce detection time and to improve our automated recovery processes.
- We're reviewing our update procedures to help catch this kind of problem during our testing cycle.
We'll publish a post-incident report within five business days."
So someone made a change and it went wrong. It happens.