What type of Ddos attack was used by "LizardSquad" group to take down PSN, Xbox and website of Malaysian Airlines ?

In Dec, 2014 a Black Hat hacker group named "LizardSquad" allegedly assaulted Sony’s and Microsoft’s servers with a distributed denial-of-service (DDoS) attack, which overwhelms a target with junk data that most servers can’t handle. The result was that PlayStation and Xbox owners couldn’t play many games or use online services for extended periods of time — potentially costing the companies millions of dollars in lost transactions and damages.