What is a DDoS attack primarily characterized by?

A Distributed Denial of Service (DDoS) attack is primarily characterized by flooding a target system with excessive traffic. This overwhelming influx of traffic prevents legitimate users from accessing the services or resources of the affected system, effectively making it unavailable. DDoS attacks typically involve multiple compromised systems that collectively send numerous requests to the target, leveraging the sheer volume of traffic to disrupt normal operations.

In contrast, the other choices describe different types of cyber threats. Unauthorized access to a database refers to gaining illicit entry to a restricted database for data theft or manipulation. The installation of harmful software, such as malware, focuses on introducing malicious programs into a system for various harmful purposes. The alteration of system configurations implies unauthorized changes to the settings of a system or network, which can lead to vulnerabilities or malfunctions. Hence, while these actions represent significant security breaches, they are not defining characteristics of a DDoS attack.