A buggy update caused a major outage across Microsoft 365 services, including Outlook, Exchange Online, and Teams, starting around 8:40 PM UTC on a Saturday evening and lasting until about 9:45 PM UTC. The disruption, attributed to a flawed code change in the authentication system, led to widespread authentication issues and service slowdowns, affecting users primarily in the US, with notable impacts in New York, Chicago, and Los Angeles. Microsoft resolved the issue by reverting the update, but not before tens of thousands of users—37,000 with Outlook and 24,000 with Microsoft 365—reported problems, as tracked by Downdetector. This incident highlights the challenges of managing large-scale cloud services.

[NOT NECESSARILY RESOLVED YET]