Which type of attack involves overwhelming a service with traffic to render it unavailable?

The type of attack that involves overwhelming a service with traffic to render it unavailable is known as a Denial of Service (DoS) attack. In this scenario, the attacker floods a target server with excessive requests, exhausting its resources and preventing legitimate users from accessing the service. This type of attack aims to disrupt the normal functionality of a service, making it inaccessible to users, which can significantly impact operations and lead to loss of revenue or damage to reputation.

Other types of attacks, such as phishing, ransomware, and SQL injection, focus on stealing information, encrypting data for ransom, or exploiting vulnerabilities in databases, respectively. While they are all serious threats, none are specifically designed to incapacitate a service through overwhelming traffic. Thus, the defining characteristic of a DoS attack lies in its objective to deny access to legitimate users by saturating the bandwidth or processing power of a target service.