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 – ONGOING

31/08/2026 09:57:00 AM

NHS.net Connect Reference: INC46922682

Microsoft Reference: DZ1463442

Issue Status: ONGOING

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

More info: When the browser hang occurs, the browser hangs indefinitely until the users exits out. This occurs before the user is able to perform the notification edits.

Current Update: 31/08/2026 09:58:00 AM – Following their review of the internal reproduction of impact and HAR logs provided by a subset of affected users, Microsoft has determined that there is a latent code regression that is causing users’ browsers to hang in Microsoft Defender for Office 365 when editing attack simulation training end user notifications and resulting in impact. They have developed a code fix to address this issue and anticipate that the deployment progress will begin prior to their next scheduled update. At which point, they aim to provide a remediation timeline.

Scope of impact: Some users who are utilising Microsoft Defender for Office 365 users editing attack simulation training end user notifications are impacted. This section may be updated as the investigation progresses.

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

Next update by: Tuesday, September 1, 2026, at 7:00 AM UTC