Answer first
Don't call the number on screen and don't type anything into the warning page. Close the browser using Task Manager (Windows) or Force Quit (Mac) if the page won't close normally, then reopen the browser separately and review recent downloads and site permissions before continuing.
Real operating system or antivirus alerts don't lock your screen and ask you to call a phone number. That pairing is one of the clearest signs of a scam page, not a genuine system message.
Some of these pages block the normal close button or force fullscreen mode. Use Task Manager (Ctrl+Shift+Esc on Windows) or Force Quit (Mac) to end the browser process instead of clicking anything on the page itself.
When you reopen the browser, avoid restoring the previous session/tab if prompted. Check notification permissions and recent downloads for anything you didn't intend to allow or install.
Keep a note of what the page said, whether a sound played, and what site or link led to it. This helps confirm it was a browser-based warning rather than an actual device issue.
Quick FAQ
Is my computer actually blocked?
Almost always no. This is typically a webpage styled to look like a system alert, not an actual lock placed by your operating system, antivirus, or internet provider.
Should I call the phone number shown on the warning?
No. Genuine operating system or antivirus alerts do not lock your screen and display a phone number to call. That combination is a common sign of a scam page.