Microsoft Defender XDR portal hit by extended outage

Bleeping Computer reports that Microsoft is currently managing a significant service disruption affecting its Defender XDR security portal, with some customers experiencing blocked access and missing functionality for over ten hours due to a traffic surge overwhelming system resources.

According to a service alert, a "spike in traffic caused high Central Processing Unit utilization" on critical backend components, leading to the outage that Microsoft has officially designated as an incident. The problems, which began earlier today, have prevented access to portal features and reportedly include missing advanced threat-hunting alerts and devices not appearing in the console. Microsoft's engineering teams have applied mitigations to increase processing throughput, and telemetry indicates that availability has recovered for many impacted organizations.

However, the company acknowledged it is still working with a small number of customers for whom the issues persist, coordinating to collect additional client-side diagnostics and HTTP Archive traces to complete its investigation. While the core cause appears to be a capacity-related traffic spike, the extended duration and impact on critical security monitoring tools highlight the operational challenges of maintaining always-on cloud services, especially for essential cybersecurity platforms where visibility gaps can pose significant risk.