A warning banner is a visible alert displayed in an application to flag a potentially risky message, link, sender, or action. It is designed to make users pause and verify before clicking, replying, sharing information, or approving a request.
In cyber security, banners add friction to attacks that rely on urgency or misplaced trust. For example, a collaboration tool may display an alert on a suspicious message from an external contact. A banner is a signal, not a verdict: it does not necessarily block or remove the message, and a warning-free message is not guaranteed safe. Users should verify unexpected requests through a separate trusted channel, while organizations should pair alerts with reporting tools and security training.