Which type of attack seeks to overwhelm a service, rendering it inoperable?

The correct choice, which identifies the type of attack that seeks to overwhelm a service and render it inoperable, is indeed a Denial-of-Service (DoS) attack. This attack method is designed to make a network service unavailable to its intended users by overwhelming it with a flood of illegitimate requests or traffic. The excessive volume of incoming requests can consume the resources of the target system, such as bandwidth or processing power, ultimately leading to a crash or prolonged downtime.

In contrast, a man-in-the-middle attack involves eavesdropping or intercepting communications between two parties, which does not primarily focus on disrupting service availability. A phishing attack is primarily aimed at tricking individuals into revealing sensitive information, such as usernames and passwords, through deceptive emails or websites. Session hijacking, on the other hand, involves taking control of a user session after they have authenticated to a service, which again does not serve the purpose of rendering a service inoperable.

Overall, the Denial-of-Service attack stands out as the specific type of attack that disrupts service usability by overwhelming it, making it the correct response to the question.