What defines a denial-of-service (DoS) attack?

A denial-of-service (DoS) attack is specifically characterized by the attempt to make a network service unavailable to its intended users. This is typically accomplished by overwhelming the service with excessive traffic or requests, consuming resources to the point that legitimate users cannot access the service. The core purpose of such an attack is to disrupt the normal functioning of the targeted service, causing it to become slow or to crash entirely.

In contrast, accessing a network without authorization pertains to unauthorized access and is more related to security breaches rather than service disruption. Distributing malicious software focuses on the dissemination of harmful programs, which does not inherently equate to making services unavailable. Unintended data loss during transmission involves issues related to data integrity and reliability, which again is distinct from the operational disruption caused by a DoS attack. The defining feature of a DoS attack is its focus on rendering a service unusable for legitimate users, which is exactly what option A captures.