What is a likely consequence of a successful denial-of-service attack?

A successful denial-of-service (DoS) attack primarily aims to disrupt the normal functioning of a targeted server, network, or service by overwhelming it with a flood of traffic or requests. This results in service unavailability, where legitimate users cannot access the services or applications they need. The primary goal of such an attack is to render the target incapacitated, affecting its ability to respond to legitimate requests, which directly aligns with the chosen answer.

In this context, increased system performance is an unlikely outcome, as a DoS attack typically causes degradation rather than improvement of performance. Additionally, while data leakage and unauthorized access are serious security issues, they are not the main outcomes of a DoS attack; instead, these issues often arise from different types of attacks that specifically target data and access controls rather than service availability. Thus, the consequence of service unavailability is the most pertinent result of a successful denial-of-service attack.