possible virus, computer locked

Restarting will work. Other methods to remove the maximized browser window:

• Press F11 to exit the browser from full screen mode, then close the tab
• Press Alt + F4 (until the browser process is terminated) or Ctrl + W (to close the tab)
• Press Ctrl + Shift + Escape to open Task Manager, locate the browser processes and right click End Task
• Hold the power button down until your computer turns off (this will always work)

After that, clear your browser's cache.

For Edge, enter edge://settings/clearBrowserData into the URL bar. Select the first three options then press Clear now

For Chrome - https://support.google.com/accounts/answer/32050?sjid=15486707136132768444-AP

Firefox - https://support.mozilla.org/en-US/kb/how-clear-firefox-cache

To minimize the likelihood of this happening again, install an Adblocker.

https://microsoftedge.microsoft.com/addons/detail/ublock-origin-lite/cimighlppcgcoapaliogpjjdehbnofhn

https://microsoftedge.microsoft.com/addons/detail/ublock-origin/odfafepnkmbhccpbejgmiehpchacaeak

https://microsoftedge.microsoft.com/addons/detail/adblock-plus-free-ad-bl/gmgoamodcdcjnbaobigkjelfplakmdhh

Further reading -

https://support.microsoft.com/en-us/windows/protect-yourself-from-tech-support-scams-2ebf91bd-f94c-2a8a-e541-f5c800d18435

https://www.microsoft.com/en-US/concern/scam