Misbehaving Microsoft Teams ad brings down the entire Windows 11 desktop

Enlarge / Windows 11 sports built-in Microsoft Teams integration that may have brought down the desktop and taskbar in a recent preview build. (credit: Andrew Cunningham)

Microsoft released a new build of Windows 11 to Windows Insiders late last week as it prepares for the operating system's release on October 5, but the first testers to install the new build quickly ran into problems-the taskbar, desktop, Settings app, and other core OS components were refusing to load. Microsoft quickly published a registry edit that resolved the problem, but the company didn't go into more detail on what went wrong.

The most thorough examination of the problem comes from developer Daniel Aleksandersen's Ctrl blog. As he explains, the "IrisService" mentioned in Microsoft's registry edit is part of the Windows Spotlight service, which is responsible for fetching new lock screen wallpapers and other suggestions and advertisements. From Aleksandersen's post:

Based on the Microsoft-provided workaround, I narrowed the problem down to a registry key that contained a serialized JSON blob. The blob contained an advertisement for Microsoft Teams. The messaging and imagery in the promotion were identical to the panel you get when you press the Windows key + C on a Windows account not already set up with Teams.

In other words, it looks like an ad for one of Windows 11's built-in apps went wrong, and most of the operating system's user interface stopped working as a result.

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