Hello Emma P,
Thank you for reaching out to the Microsoft Community. My name is Gunasekar and I'm happy to help.
Treat all unsolicited phone calls/ emails with skepticism. Do not provide any personal information. If you receive an unsolicited call from someone claiming to be from Microsoft, please hang up or if it's an email please ignore it.
Do not click any links on the screen (or) call the number. Just follow the steps below to disable the screen.
- Click CTRL + ALT + DELETE keys altogether.
- Open Task manager.
- Select the browser running on the lists and click End tasks.
- The pop up should disappear.
However, it is recommended to keep your Microsoft account safe and secure by following the suggestions below.
- Create a strong password.
- Enable two-factor authentication.
- Delete unused devices from your account.
Related article for your reference:
https://support.microsoft.com/help/628538c2-7006-33bb-5ef4-c917657362b9
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I hope this information helps. If you have any questions, please let me know and I will be happy to help you further.
Best regards,
Gunasekar N