References are listed below:

US patent application publication, Application number - US 13/458,129 - System and method for mitigating application layer distributed denial of service attacks using human behavior analysis

https://www.google.com/patents/US20130291107

Akamai’s [state of the internet] / security - Q1 2015 State of the Internet — Security Report

Analysis of the Global Distributed Denial of Service (DDoS) Mitigation Market - Frost & Sullivan’s Global DDoS Mitigation Market Research Report, July, 2014

2015 Data Breach Investigations Report – Verizon