This tactic of sending unsolicited messages and calls via Teams has an easy solution—only allow specific external domains to communicate with your end users. Review your Teams logs, see which domains your users are communicating with, add them to the allow list and enable the control. Make your end users open up a support ticket for future domain adds so you can vet them.
[#]Cybersecurity
This is unfortunately another example of #Microsoft INsecure by default, as they allow messages and calls from any domain by default and leave it up to the organization to manage.
Microsoft docs:
https://learn.microsoft.com/en-us/microsoft-365/solutions/trusted-vendor-onboarding?view=o365-worldwide#allow-the-vendors-domain-in-teams-external-access
From: @BleepingComputer
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