What is the main purpose of User Account Control (UAC)?

User Account Control (UAC) is primarily designed to limit the privileges of software applications, which enhances the overall security of the Windows operating system. By controlling the permissions that applications have, UAC helps to prevent malware from gaining elevated access to the system without user consent. When a program requires administrative level access to make changes that could potentially affect the computer, UAC prompts the user for permission. This ensures that only authorized changes take place, thereby minimizing the risk of unauthorized modifications to the system.

The other options relate to different aspects of system management or security but do not capture the core functionality of UAC. For example, while encryption of account data is crucial for protecting sensitive information, it is not the primary role of UAC. Similarly, UAC is not focused on facilitating user authentication; rather, it reacts to programs attempting to execute with higher privileges. Lastly, improving network speed is outside the scope of UAC's functionality, as it pertains to network management rather than user privilege management.