Which of the following contains information that is read by a Web application whenever a user visits a site?

PII (Personally Identifiable Information) is a classification category for sensitive data about individuals, not a file or mechanism that web applications read on site visits.

A cookie is a small piece of data sent by a web server to a user's browser, which stores it and automatically sends it back on subsequent requests to the same site. Web applications read cookies to maintain session tokens, authentication state, and user preferences, making them the primary mechanism for stateful web interactions.

A rootkit is malware that provides persistent, hidden privileged access to a compromised system and has no role in normal web application data exchange.

DiD (Defense in Depth) is a layered security strategy concept, not a data storage or retrieval mechanism used by web applications.