Regarding the "FCM Messages Test Notification!!!!" for Teams and Hangouts

[Ink]

The Microsoft 365 Status Twitter account states that the issue only affected Android devices. Thursday afternoon, the account shared that Microsoft had "isolated the source of the issue and applied a mitigation."

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Microsoft stops strange 'FCM Messages' notifications on Microsoft Teams

People received random test notifications on Microsoft Teams yesterday.

www.windowscentral.com

Last week a vulnerability was published for Firebase Cloud Messaging (FCM), which many of Google's apps, including Hangouts, use to deliver notifications. The vulnerability allows someone to exploit FCM keys stored in APK files in order to broadcast messages to anyone using a Firebase-based application — in this case, Hangouts.

Yesterday, some Hangouts users received a suspicious "Test Notification!!!!" alert labeled "FCM Messages." Tapping the message opens the Hangouts conversation list, with no sign of this strange alert anywhere to be seen.

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Hangouts users shouldn't panic about mysterious 'FCM' notifications

The mass messages are likely tied to recent reporting on Firebase exploits

www.androidpolice.com