[Cyber Security Terms](/glossary) DDoS Attack [Blog](/blog)[Breaches](/breaches)[Resources](/resources)[News](/news) [Cyber Security Terms](/glossary) # DDoS Attack ##### [Edward Kost](/team/edward-kost) updated Sep 13, 2021 ###### Contents ## What is a DDoS Attack? A [Distributed Denial-of-Service (DDoS) attack](https://www.upguard.com/blog/what-is-a-ddos-attack) is an attempt to overwhelm a web server with fake internet traffic with the objective of forcing it offline. DDoS attacks are executed by compromised devices networked together to [create a botnet](https://www.upguard.com/blog/what-is-a-botnet). Any device can become a bot if it’s infected with a specific malware - usually Mirai malware. Examples of devices that could be turned into bots include computers, mobile devices, and Internet of Things (IoT) devices. Bots divert a small amount of traffic from infected devices to avoid detection. As each bot is networked together, the intensity of the attack increases. This is why DDoS attacks require large-scale botnets. ## How Do Botnets Work? Botnets receive two different sets of instructions: 1. How to locate and infect other devices 2. DDoS attack details  The method of delivery of these instructions depends on how the bots are networked together. There are two different arrangements - the client-server model and the P2P model. ### Client-Server Model This is the most common botnet arrangement. Each infected device is orchestrated from a single point of origin known as the Command and Control server (C\&C server). This is where all DDoS instructions are issued from. ### P2P Model In a P2P model, each bot receives its instructions from other infected bots on the network. Because there isn’t a single source issuing commands, this type of botnet is more difficult to take down. ## Examples of Famous DDoS attacks Five examples of famous DDoS attacks include: 1\. [The Google DDoS Attack ](https://blog.google/threat-analysis-group/how-were-tackling-evolving-online-threats/)(2017) 2\. [KerbsonSecurity DDoS Attack](https://krebsonsecurity.com/2016/09/krebsonsecurity-hit-with-record-ddos/) (2016) 3\. [GitHub DDoS Attack](https://www.wired.com/story/github-ddos-memcached/) (2018) 4\. [PopVote DDoS Attack](https://www.forbes.com/sites/parmyolson/2014/11/20/the-largest-cyber-attack-in-history-has-been-hitting-hong-kong-sites/?sh=696300d838f6) (2014) 5\. [Cloudflare DDoS Attack](https://www.cnbc.com/2014/02/11/record-breaking-ddos-attack-strikes-cloudflares-network.html) (2014) ## Key takeaways * Many victims are unaware that their devices have been recruited into a botnet. * One of the leading causes of IoT devices becoming infected with botnet malware is the use of default usernames and passwords. * A 503 server unavailable message could be evidence of a DDoS attack taking place. * * ###### Reviewed by No items found. ###### Author ##### [Edward Kost](/team/edward-kost) ###### Reviewed by ##### [Kaushik Sen](/team/kaushik-sen) ###### Join 27,000+ cybersecurity newsletter subscribers ## Read more about DDoS Attacks Learn more about DDoS Attack and the latest issues in cybersecurity. [UpGuard](/blog/what-is-a-botnet) [What is a Botnet? You Might Be Infected Right Now](/blog/what-is-a-botnet) #### [What is a Botnet? 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