Is a pop-up saying my computer is infected and to call a number real?

Tech-support scam pop-ups are designed to look like Windows or macOS system alerts or antivirus warnings. They typically play an audio warning, fill the screen, and display a phone number. Calling the number connects you to scammers who claim to be Microsoft, Apple, or an antivirus company. They ask for remote access to your computer, show you 'evidence' of infection using normal system tools, then demand payment for a fix or a support contract. Sometimes they install actual malware during the session. Windows and macOS do not display warning pop-ups with phone numbers. Close the browser tab or reboot your computer to dismiss the pop-up.

Everything about the pop-up is engineered to prevent calm thought: the siren audio, the flashing warnings, the countdown, the full-screen lock that hides your browser controls. It looks like a system failure, but it is only a web page — usually reached through a malicious ad or a mistyped address — and it has no ability to inspect your machine or detect any infection.

The phone call is where the real damage happens. Once connected, the 'technician' takes remote control, stages fake evidence in system logs, and pushes for payment — and remote sessions have been used to install malware, harvest saved passwords, or drain bank accounts while the victim watches a blank screen. If remote access was granted, treat every credential used on that machine as compromised.