Which FortiGate feature helps in preventing unauthorized access to sensitive data?

Data Loss Prevention (DLP) is specifically designed to protect sensitive data from unauthorized access and potential leaks. It achieves this by monitoring, identifying, and controlling sensitive information, ensuring that it is not improperly shared outside of an organization. DLP employs policies that can detect data patterns, such as credit card numbers or personal identifying information, and can enforce rules to either block such transmissions or alert administrators when sensitive data is at risk of being exposed.

While the other features like Intrusion Prevention System, Web Filtering, and Firewall Rules contribute to the overall security posture by preventing attacks, controlling web access, and filtering traffic, they do not have the same focused capability on preventing the loss of sensitive data as DLP does. DLP's specific functionality in protecting and ensuring compliance around information security makes it the most relevant choice for preventing unauthorized access to sensitive data.