You’re browsing along, and a window takes over your screen. Beeping. A red warning. Your computer has been infected with 5 viruses. Do not turn off your computer. Call Microsoft Support. Sometimes the page goes full-screen and the back button stops working.
If you call, a polite technician asks to remote in to fix the problem. The moment they have control of your computer, they can install whatever they want, watch you log into your bank, lock your files, and then demand payment to remove the virus they put there.
This works because the screen looks broken and the voice on the phone sounds calm. The contrast is the trap.