A web page says your PC is infected. Is the alert real?

A page that fills the screen, makes noise or displays a phone number is not a Windows Security diagnosis. Microsoft says its genuine error and warning messages do not include phone numbers. Do not call the number, install the offered tool or grant remote access.

Check without trusting the page​

1. Try closing the tab. If the page traps the browser, close the browser from your operating system and reopen it without restoring that tab.
2. Open Windows Security from the Start menu, not from a button inside the page. Check Virus & threat protection → Protection history for an actual detection.
3. If you downloaded or ran anything, update the protection software and run a scan. Check installed apps and browser extensions for anything you did not authorize.

Use the result​

No Windows Security detection and you only viewed the page? Close it and remove any site-notification permission it persuaded you to grant. A real detection appears? Read its file name, status and recommended action in Windows Security. You called, paid or gave remote access? Disconnect the remote session, contact your bank if you paid, and secure accounts from a trusted device.

Avoid clicking “Allow” to make the warning disappear. Microsoft's tech-support scam guide explains this full-screen browser trick. A quiet Protection history does not prove the computer is clean after a file was run; a scan and follow-up are still warranted.

If the tab will not close​

Use the operating system's window switcher or Task Manager to close the browser. When it restarts, decline to restore the suspicious tab. If you allowed notifications, remove that site's permission in browser settings so the warning cannot keep appearing after the page is gone.