An overlay window is a user interface element drawn on top of another app’s screen. On mobile devices, especially Android, overlays can be legitimate features such as chat heads, pop-ups, or accessibility aids. In malicious hands, they become a way to hide the real interface and replace it with something deceptive.
In cyber security, overlays matter because they can support phishing, tapjacking, and payment fraud. A fake login prompt or confirmation dialog can sit above a banking app and trick the user into entering credentials or approving a transfer. Attackers may also use overlays to block warnings, obscure security prompts, or make a fraudulent screen look like the trusted app underneath. Defenders watch for unusual overlay permissions, unexpected accessibility behavior, and sensitive apps that refuse to operate when their screen is obscured.