Microsoft 365 Alert – Service Degradation – Microsoft Defender XDR – Users’ browsers hang in Microsoft Defender for Office 365 when editing attack simulation training end user notifications – RESOLVED

31/08/2026 09:57:00 AM

NHS.net Connect Reference: INC46922682

Microsoft Reference: DZ1463442

Issue Status: RESOLVED

Issue Description: Users’ browsers hang when editing Microsoft Defender for Office 365 attack simulation training end user notifications.

More info: When the browser hang occurred, the browser would hang indefinitely until the users exit out. This occurred before the user was able to perform the notification edits.

Final Update: 01/09/2026 10:18:00 AM – Microsoft has completed the development and deployment of their code fix and confirmed that impact has been successfully remediated.

Scope of impact: Some users who were utilizing Microsoft Defender for Office 365 editing attack simulation training end user notifications were impacted.

Root cause: A latent code regression caused users’ browsers to hang in Microsoft Defender for Office 365 when editing attack simulation training end user notifications and resulted in impact.

Next steps: Microsoft is working to better understand the underlying cause of the latent code regression so that they can prevent similar issues from happening in the future and make the service more resilient.