Microsoft Outage: Was It Caused By A Cyberattack Or Server Failure? Executive Clarifies

Microsoft has said its latest attempts to restore services affected by a global outage have not produced the expected results, as it continues to deal with server failures across its infrastructure. The disruption, which began on Thursday, November 12, has affected Outlook, Copilot and several Microsoft 365 applications, while Teams users have reported problems with calendar access and meeting scheduling.

The disruption centres on Exchange Online, Microsoft's cloud-based email service, with problems affecting other applications that depend on its infrastructure. The company has been restarting affected servers and redirecting traffic, but some servers that initially returned to service became unresponsive again when traffic was restored. This reduced the number of servers available to handle requests, complicating recovery efforts.

What Caused The Microsoft Outage

Microsoft traced the disruption to an overloaded process on affected servers responsible for establishing secure connections. When the process becomes overwhelmed, the servers stop processing requests, reducing available capacity and shifting additional traffic onto the remaining infrastructure.

The company is testing a configuration change to address the issue while restarting affected servers. It has also begun reverting a recent network configuration change that correlated with the start of the disruption. Microsoft is restricting certain types of traffic in specific locations and rebuilding some affected servers using an earlier software configuration to test whether this prevents them from becoming unresponsive.

Microsoft Says No Sign Of Cyberattack

Microsoft's Executive Vice President of Copilot, Agents, and Platform apologised to customers affected by the disruption and said there was no indication that the outage resulted from malicious or cyber activity.

"We regret that today’s outages caused disruptions for our customers, and we are working to address the issue. We will continue to share more information as soon as we have it, and for now I can confirm that there is no indication this is the result of malicious or cyber activity," the executive said.

The outage also disrupted Microsoft 365 connectors used by OpenAI and Anthropic. OpenAI said problems could prevent new connections and affect some tools, while Anthropic separately reported an issue with an upstream provider affecting its Microsoft 365 connector.

Reuters reported that Downdetector recorded more than 130,000 user reports of Outlook problems at the peak of the disruption on Thursday. Microsoft said it was monitoring affected servers and would gradually restore additional traffic as stability improved. The company had not provided a confirmed timeline for full service restoration.