Correct Response: C. A proxy server acts as an intermediary between the computers on an organization's network and the Internet. This guards the IP addresses of the individual computers from being visible from outside of the organization. A, B, and D are incorrect because a proxy server is not involved in the backing up of files (A), the balancing of network traffic loads (B), or the blocking of threatening data from the Internet (D). These functions are typically carried out by network hard drives or cloud back-up services, routers, and firewalls respectively.