While you browsing the web, you may occupationally run into infection warnings that appear to be legitimate but aren’t. These anti-malware warning messages – appropriately called “scareware” -are designed to scare you to call 1-800-number,so they scam you further.
Just stay calm, just hold keys “Alt” key + “Tab” to switch between applications windows to save all your works like Microsoft Word, Microsoft Excel, etc, then reboot your PC. After the PC reboot, just clean the browser catch, and reset the setting of that browser, or all browser, likely Microsoft Edge, Google Chrome, or Firefox
How to clean browser catch, and default setting reset click here?
Fake malware alert look similar like the image below: