Denial-of-service attack

A denial-of-service attack makes a computer system, network, or service unavailable to legitimate users by disrupting or overwhelming its resources.

Distributed denial-of-service: A denial-of-service attack launched from many systems, often coordinated through a botnet. Multiple sources multiply traffic and make blocking an attack more difficult.
Denial-of-service vulnerability: A software or system flaw that allows an attacker to make a service unavailable. A vulnerability is an exploitable weakness; an attack is the action that disrupts availability.
DDoS mitigation: Techniques and services that detect, absorb, filter, or reroute denial-of-service traffic. Mitigation aims to preserve legitimate access while an attack is underway.
Availability (information security): The property that authorized users can access information and systems when needed. Denial-of-service attacks directly violate this security objective.
Botnet: A network of compromised devices controlled remotely, often without their owners’ knowledge. Attackers use botnets to generate traffic from many distributed sources.
Intrusion (computer security): Unauthorized access to a computer system or network. Intrusion seeks access, while denial of service primarily targets availability.
Content delivery network: A distributed network of servers that delivers web content closer to users. Distributed capacity can absorb traffic and reduce pressure on an origin server.
Business continuity: An organization’s ability to maintain or restore essential operations during disruption. Availability attacks can interrupt services that continuity plans must sustain.
SYN flood: A TCP denial-of-service attack that sends connection requests without completing the handshake. It can consume a server’s connection state by leaving requests unfinished.
Ransomware: Malware that denies access to data, commonly by encrypting it, and demands payment. Ransomware blocks data access through malware rather than necessarily overwhelming a service.

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