A browser lock screen is a page or overlay that makes a web browser look frozen, trapped, or unusable. It may cover the page with a full-screen warning, disable obvious controls, or loop pop-ups so the user feels unable to close the tab. In many cases, the browser is not truly locked at the operating-system level; the attacker is using design tricks to create the impression of a serious problem.
This tactic matters because it turns fear into compliance. Attackers use it in tech support scams, fake security alerts, and malicious ad campaigns to push victims into calling a number, installing remote-access software, or entering credentials. Defenders look for the social-engineering effect, not just malware indicators: users should close the browser with trusted controls, avoid calling numbers shown on-screen, and treat unexpected warnings as untrusted until verified through official support channels.