(Update: the login services came back after 5 hours)
This afternoon (Pacific time) about 2:30pm, some Microsoft 365 services, including logins to Microsoft 365 "work or school" accounts and the Azure Portal, went down, failing to authenticate and returning a number of error messages instead. Status.office.com began reporting problems, saying users could be "unable to access Outlook.com, Microsoft Teams including Teams Live Events, and Office.com. Additionally, Power Platform and Dynamics365 properties are affected by this incident." The status report was then updated to say that a recent change may have affected logins, and that the company was rolling back the change. However, the report was updated again, saying:
Current status: We've identified that reverting the recent change did not alleviate impact to Microsoft services as expected. We're working to explore additional options for mitigation.
The outage is affecting login services, and Azure Virtual Machines (like the one we're running here at OnMSFT.com) and other Azure services are unaffected, although it's not possible to log in to the Azure Portal, or to connect to other Microsoft 365 services. We're currently connected to our Teams account, and it's running fine, but an attempt to log in to the service would likely fail.
These outages do happen from time to time with almost all online services, and reporting them is sometimes more trouble than it's worth, as the services come back up before we're able to report on the outage. It's been two hours now, however, and appears to be widespread.