Distributed denial-of-service attack (DDoS)

A distributed denial-of-service (DDoS) attack floods a target with traffic from many sources to make it slow or unreachable.

Format
Security & Encryption
Updated
Updated
Glossary Security & Encryption
Distributed denial-of-service attack Also known as DDoS.Aliases: DDoS attack, denial of service, DoS.

Definition

A distributed denial-of-service (DDoS) attack floods a target with traffic from many sources to make it slow or unreachable.

How it works

Attackers typically point a botnet — thousands of compromised machines — at one target, exhausting its bandwidth, connection capacity, or application resources. Because the traffic comes from everywhere at once, blocking individual addresses achieves little. Effective defenses filter or absorb the flood upstream, which is why DDoS protection is usually a network or CDN-level service rather than something one server does for itself.

Example: A volumetric attack can push more traffic at a site than its network link can carry, taking it offline without touching a single vulnerability.

Often confused: A DDoS overwhelms a service with traffic; hacking implies intrusion. A site under DDoS is not breached — it is buried.

Sources

Last reviewed 2026-07-19.