No self-respecting DDoS attacker would fail to spoof the User-Agent. This is even Web Scraping 101. Attacks these days are getting rather sophisticated, where

No self-respecting DDoS attacker would fail to spoof the User-Agent. This is even Web Scraping 101. Attacks these days are getting rather sophisticated, where significant amount of attacks are using javascript enabled headless browsers. (http://www.darkreading.com/attacks-breaches/ddos-attack-used-headless-browsers-in-15/240162777 http://www.darkreading.com/attacks-breaches/ddos-attack-used...)