Which of the following best describes a zombie computer?

A zombie computer refers to a device that has been compromised and is being controlled remotely by a hacker, often without the owner's knowledge. This type of computer is typically part of a larger network of compromised machines known as a botnet, which can be used to perform various malicious activities, such as sending spam emails, conducting distributed denial-of-service (DDoS) attacks, or distributing malware.

The defining characteristic of a zombie computer is its malicious control, which distinguishes it from other types of computers. For instance, a computer with high uptime does not imply any malicious or compromised status; it simply indicates that the system is operational for long periods. Similarly, while a computer used for performing network tasks or running application software can fulfill legitimate roles, these functions do not relate to malicious control or compromise by an attacker. Therefore, the true essence of a zombie computer lies in the unauthorized control exerted by a hacker, making the identification of option C as correct.