In the lifecycle of a Spring Boot application, configuration files play a central role in defining the application's behavior. But what happens when these files contain sensitive data, such as database credentials, API keys, or secrets for third-party services? Without proper handling, this data could be exposed, leading to catastrophic breaches. This article dives deep into securing sensitive data within Spring Boot’s application.properties or application.yml files, especially when working with launch configurations. We’ll explore best practices, practical examples, and why this focus is essential for robust application security.