Which of the following best defines a Denial of Service (DoS) attack?

A Denial of Service (DoS) attack is best defined as the act of overwhelming a service, such as a website or server, to render it unavailable to legitimate users. This type of attack typically involves flooding the target with an excessive amount of requests or data, which exhausts the resources or bandwidth, making it impossible for the service to respond to legitimate traffic. The goal is to disrupt the normal functioning of the service, deny access to legitimate users, and cause downtime or loss of service.

In contrast, unauthorized data access pertains to situations where an attacker gains access to data they should not see, which doesn't specifically involve making a service unavailable. Tricking a user into providing personal information relates to social engineering or phishing attacks, while installing malicious software pertains to malware attacks that compromise systems but do not necessarily equate to a denial of service. Each of those other options addresses different cyber threats and attack methodologies, distinctly separate from the primary intent and action involved in a DoS attack.