What is a denial of service attack?

A denial of service attack is characterized by a deliberate attempt to block access to a network service or resource, rendering it unavailable to legitimate users. This often occurs when a large number of computers, sometimes controlled as part of a botnet, flood the target computer or network with excessive requests. The overload prevents legitimate users from accessing the service, thereby disrupting operations and causing significant inconvenience or harm to the affected entity.

The essence of a denial of service attack lies in its goal of overwhelming the system, not necessarily requiring access to it. It focuses on exploitation through sheer volume and traffic, rather than data corruption or unauthorized access. In contrast, other options describe different types of cyber threats, such as the sending of numerous messages by a single computer or unauthorized access, which do not align with the primary objective and mechanism of a denial of service attack.