Hi,
This is FAKE and SCAM for sure.
Are you seeing this in a webpage?
Do NOT enter any information and never contact the number and NEVER share any data.
Press Ctrl+Alt+Del and from menu click to open task manager and if it work, try close the task which could be associate to this warning or you may close all browsers.
You may also press the power button once and it should shutdown your PC and then turn on your PC to see if the warning exists?
It is also good idea if you disconnect from the internet.