Miscreants who earlier this week took down servers for League of Legends, EA.com, and other online game services used a never-before-seen technique that vastly amplified the amount of junk traffic directed at denial-of-service targets.

Rather than directly flooding the targeted services with torrents of data, an attack group calling itself DERP Trolling sent much smaller sized data requests to time-synchronization servers running the Network Time Protocol (NTP). By manipulating the requests to make them appear as if they originated from one of the gaming sites, the attackers were able to vastly amplify the firepower at their disposal. A spoofed request containing eight bytes will typically result in a 468-byte response to a victim, a more than 58-fold increase.

"Prior to December, an NTP attack was almost unheard of because if there was one it wasn't worth talking about," Shawn Marck, CEO of DoS-mitigation service Black Lotus, told Ars. "It was so tiny it never showed up in the major reports. What we're witnessing is a shift in methodology."

The technique is in many ways similar to the DNS-amplification attacks waged on servers for years. That older DoS technique sends falsified requests to open domain name system servers requesting the IP address for a particular site. DNS-reflection attacks help aggravate the crippling effects of a DoS campaign since the responses sent to the targeted site are about 50 times bigger than the request sent by the attacker.

During the first week of the year, NTP reflection accounted for about 69 percent of all DoS attack traffic by bit volume, Marck said. The average size of each NTP attack was about 7.3 gigabits per second, a more than three-fold increase over the average DoS attack observed in December. Correlating claims DERP Trolling made on Twitter with attacks Black Lotus researchers were able to observe, they estimated the attack gang had a maximum capacity of about 28Gbps.

NTP servers help people synchronize their servers to very precise time increments. Recently, the protocol was found to suffer from a condition that could be exploited by DoS attackers. Fortunately, NTP-amplification attacks are relatively easy to repel. Since virtually all the NTP traffic can be blocked with few if any negative consequences, engineers can simply filter out the packets. Other types of DoS attacks are harder to mitigate, since engineers must first work to distinguish legitimate data from traffic designed to bring down the site.

Black Lotus recommends network operators follow several practices to blunt the effects of NTP attacks. They include using traffic policers to limit the amount of NTP traffic that can enter a network, implementing large-scale DDoS mitigation systems, or opting for service-based approaches that provide several gigabits of standby capacity for use during DDoS attacks.