What is a DDoS - Distributed Denial of Service?

Distributed Denial of Service (DDoS) is a form of cyberattack in which multiple compromised systems work together to disrupt an online service, server or network by overwhelming the target with malicious traffic.

These attacks temporarily disrupt online services by targeting machines or resources with superfluous requests (from many sources) and overloading systems to prevent legitimate requests from being fulfilled. DDoS attacks can be particularly damaging for organizations that conduct a substantial amount of business on web platforms, such as eRetailers or financial services companies. 

Common types of DDoS attacks are: UDP flood, ICMP (Ping) Flood, SYN Flood, Ping of Death, Slowloris, NTP Amplification, and HTTP Flood. Often, large enterprises with high profile sites are targeted (banks, credit card companies and payment gateways).