A Distributed Denial of Service (DDoS) attack is an attempt to make an online service unavailable by overwhelming it with traffic from multiple sources. They target a wide variety of important resources, from banks to news websites, and present a major challenge to making sure people can publish and access important information.
http://www.digitalattackmap.com/#anim=1&color=0&country=ALL&list=0&time=16567&view=map
DDoS Attack Map