You are seeing a fake warning, generated by a website.
Press all these keys at the same time:
If you are seeing a message you have a virus (or something similar), 99.99999% of the time it’s a fake webpage intended to scare you, and ultimately convince you to install malware on your computer.
Notice the nonsense URL at the top of the window:
Ctrl-Shift-W will close the window, and you can re-open your web browser and continue with your day.
