What is the term for an attack where a user or malicious software makes a web server unavailable to legitimate users?

The term for an attack that makes a web server unavailable to legitimate users is known as a Denial of Service (DoS) attack. In a DoS attack, the attacker overwhelms the server with excessive requests or sends malformed data, which causes the server to slow down significantly or crash entirely. This disruption prevents legitimate users from accessing the service, effectively denying them service.

While a Denial of Service attack refers to attacks that can originate from a single source, there are more sophisticated variations like Distributed Denial of Service (DDoS) attacks, in which multiple systems are used to flood the target server with traffic. However, the fundamental concept of denying service remains the same in both cases. Recognizing this distinction helps in understanding the broader spectrum of attack types and their mechanisms.