What type of attack is characterized by overwhelming a server with excessive traffic?

The answer is B, as a Distributed Denial of Service (DDoS) attack is specifically designed to overwhelm a server with an excessive amount of traffic. In this type of attack, multiple compromised systems often work in concert to flood a target with requests, thereby consuming its resources and making it unavailable to legitimate users. This can lead to service interruptions, crashes, or significantly slowed performance.

DDoS attacks leverage the fact that servers can only handle a certain volume of requests at one time. When the traffic exceeds this threshold, the server may become overwhelmed and unable to respond appropriately to genuine requests. The sophisticated nature of DDoS attacks often involves using a botnet, where numerous devices across the internet are hijacked to generate the attack traffic.

In contrast, the other types of attacks listed serve different purposes: phishing attacks aim to deceive users into giving away sensitive information; SQL injection exploits vulnerabilities in a database query to manipulate or steal data; and XSS attacks involve injecting malicious scripts into web pages viewed by users, rather than overwhelming server resources. Each of these has distinct characteristics and objectives that differentiate them from a DDoS attack.