Since 2013, Hackers have adopted new tactics to boost the sizes of Distributed Denial of Service (DDoS) attack known as ‘DrDoS’ The attack exploits security weaknesses in the Domain Name System (DNS) Internet protocol. Using Internet protocol spoofing, the source address is set to that of the targeted victim, which means all the replies will go to the target and the target of the attack receives replies from all the DNS servers that are used. The impact on Internet service providers (ISPs) is four times because amplification attacks generates malicious traffic that not only consume bandwidth, but also cause support costs and impact the reputation of the ISPs, Nominum said.
Source: https://thehackernews.com/2014/04/millions-of-vulnerable-routers-aiding_3.html