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Vol. 1 · Ed. 2026
CyberGlossary
Entry № 366

Distributed Denial-of-Service (DDoS) Attack

Reviewed byCybersecurity entrepreneur & security researcher

What is Distributed Denial-of-Service (DDoS) Attack?

Distributed Denial-of-Service (DDoS) AttackA denial-of-service attack carried out from many distributed sources simultaneously — typically a botnet — to overwhelm a target's bandwidth, infrastructure, or application.


A DDoS attack uses many compromised hosts (a botnet), open reflectors, or rented stresser/booter services to flood a victim with traffic or requests from many sources at once, making it hard to filter and easy to overwhelm capacity. Attacks span layers: volumetric attacks fill links (often via amplification), protocol attacks exhaust stateful devices like firewalls or load balancers, and application-layer attacks target costly endpoints with apparently legitimate requests. DDoS is commonly used for extortion, hacktivism, competitive sabotage, or as cover for other intrusions. Mitigation relies on high-capacity scrubbing networks, anycast, on-prem and cloud DDoS protection services, behaviour-based rate limiting, and well-rehearsed incident playbooks.

Examples

  1. 01

    A 1.5 Tbps Mirai-style botnet floods a DNS provider with UDP traffic, knocking dependent sites offline.

  2. 02

    An HTTP/2 "Rapid Reset" flood from thousands of clients exhausts a load balancer's CPU.

Frequently asked questions

What is Distributed Denial-of-Service (DDoS) Attack?

A denial-of-service attack carried out from many distributed sources simultaneously — typically a botnet — to overwhelm a target's bandwidth, infrastructure, or application. It belongs to the Attacks & Threats category of cybersecurity.

What does Distributed Denial-of-Service (DDoS) Attack mean?

A denial-of-service attack carried out from many distributed sources simultaneously — typically a botnet — to overwhelm a target's bandwidth, infrastructure, or application.

How do you defend against Distributed Denial-of-Service (DDoS) Attack?

Defences for Distributed Denial-of-Service (DDoS) Attack typically combine technical controls and operational practices, as detailed in the full definition above.

What are other names for Distributed Denial-of-Service (DDoS) Attack?

Common alternative names include: DDoS.

Related terms

See also