A browser warning gives you a support number to call

A web page can display a full-screen warning, loud sound or urgent telephone number while pretending to be an operating-system alert. Its goal is to move you into a call where someone requests remote access and payment. A search advertisement can also promote a fake support number. The presence of a logo or alarming text does not make the number genuine.

Regain control without calling​

1. Do not dial the number, install a remote-control app or enter payment information. Try closing the browser tab. If it traps the tab, use the browser or operating system's normal force-quit control, then reopen without restoring the suspicious page.
2. If the warning referred to a subscription or charge, check your real card statement and vendor account separately. Type the vendor address yourself or use a saved official app, not the page's link or phone number.
3. If you gave remote access, disconnect the computer from the internet, end the remote session and seek trusted help to inspect installed remote-control software. Change affected passwords from a clean device and contact the bank if payment data was exposed.
4. Save the page URL, phone number and any charge record for reports, then report the scam. Avoid buying a “cleanup” from another unsolicited caller.

A real security warning still needs independent verification​

The FTC's tech-support scam guide says scammers use search ads, popups and fake renewals, then ask for remote access. It recommends contacting a company through a number you already know is real. If an actual security product later reports a threat inside its own interface, review that alert there. Closing a web page is not a substitute for checking a device you handed over to a stranger.