Malicious scripts are JavaScript or similar code inserted into a browser session to do something the user did not intend. They may steal credentials, capture form data, redirect traffic, modify page content, or quietly load more payloads. Because scripts run inside the browser, they can act with the privileges of a trusted website and are often hard for users to notice.
In cyber security, malicious scripts matter because they turn a normal web visit into an attack surface. They are common in web skimming, session hijacking, phishing overlays, and supply chain compromises where a trusted service, tag, or edge component injects code before the page loads. Defenders look for unexpected script changes, content security policy violations, unusual third-party domains, and unauthorized deployments. Strong authentication, scoped credentials, code review, and monitoring for response tampering help stop script injection before it reaches browsers.