A popup says my computer is infected and tells me to call support. Is it real?

Reviewed answer

A surprise web warning with a support number is usually a tech-support scam.

Do not call the number or interact with the page's buttons.
Close the tab. If necessary, quit the browser using Task Manager on Windows or Force Quit on Mac.
Reopen the browser without restoring the suspicious tabs. If you granted remote access, disconnect the device and contact its maker's support.

Get help if

You gave the caller access, disclosed financial information, or installed a program they requested.