DDoS defense and mitigation challenges:

In their quest to maximize downtime and damage, cyber criminals and hacktivists are using increasingly sophisticated Distributed Denial-of-Service (DDoS) attack methods to detect and circumvent enterprise defenses. Widely accessible DIY malware kits, such as Dirt Jumper, sell for as little as $150 in the black market and can be used to customize botnets capable of carrying out such sophisticated DDoS attacks. As the total number of DDoS attacks continues to increase, the evolution of DDoS botnet capabilities to bypass DDoS mitigation methods will likely fuel the already growing fire of DDoS attacks upon enterprises.

via Sophisticated DDoS Botnets Bypass Defenses – Cyveillance Blog – The Cyber Intelligence Blog.
I recommend taking a look at the references in the article.

Be nice with what you write.