Hi kelly,
I'm Dyari. Thanks for reaching out. I will be happy to assist you in this regard.
It does not seem it is from Microsoft. Where and when do face this warning? would you please take a screenshot with your smart phone and post it back?
If it is a pop-up window comes up when you are open browsers, it would be a scam never click on it and never call any phone number that appears on it.
Then, try the following steps to protect your computer:
1-Check for updates:
Go to Settings > Update and Security > Check for update > install all the pending updates
2- Scan for viruses & malware with the free Malwarebytes:
https://www.malwarebytes.com/mwb-download
3-Change all of your accounts passwords and enable 2 Step Verification on your accounts:
https://support.microsoft.com/en-us/windows/cre...
4-Protect yourself from tech support scams:
https://support.microsoft.com/en-us/windows/pro...
5-More steps to keep your computer secure:
https://support.microsoft.com/en-us/windows/kee...
Please let me know if you need further assistance and keep me updated.
Stay safe
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Standard Disclaimer: There are links to non-Microsoft websites. The pages appear to be providing accurate, safe information. Watch out for ads on the sites that may advertise products frequently classified as a PUP (Potentially Unwanted Products). Thoroughly research any product advertised on the sites before you decide to download and install it.