Chinese police have detained four suspects for online hacking activities which eventually led to temporary but widespread failure of Internet access in China on May 19, the Ministry of Public Security said Tuesday.

The ministry said the suspects were detained on May 29 following police investigations in Jiangsu, Zhejiang and Guangdong provinces.

Giving no more details than surnames of two suspects, Xu and Wang, the ministry said the suspects allegedly launched a Distributed Denial of Service (DDoS) attack against the servers of DNSPod, a Chinese DNS (domain name system) provider and domain registrar.

The DNS is what computers use to find each other on the Internet. A DNS attack targets thousands or tens of thousands of compromised computers and uses them to flood a server with bogus data packets until all of its available resources are consumed trying to process them. This swamps the server, making it unresponsive to everyone using it.

According to the ministry, the motive for the attack was fierce business competition between unauthorized online gaming service providers, which attracted gamers from official providers with less limited and free access.

In order to sabotage other "competitors", the suspects launched the attack against DNSPod, which provides access to some of those unauthorized gaming sites.

The attack triggered a chain reaction because DNSPod's servers were also used by Baofeng, a highly popular Chinese video streaming service. Once millions of Baofeng users submitted their video application, their unanswered DNS requests were passed on to higher-level servers that didn't know how to process them.

The requests piled up, and the resulting traffic jam slowed or halted Internet access, Baofeng said Monday.

Internet users in more than 20 provinces were affected on May 19, the ministry said. It was described as the worst Internet incident in China, with nearly 300 million users, only after a service interruption due to damaged undersea cables during an earthquake near Taiwan on December 26, 2006.

Internet access returned to normal several hours later. But the incident caused wide calls in China for increasing safety measures of Internet.

Baofeng company Monday announced it would recall 120 million online video playing software whose faulty design was believed to have automatically caused continuous requests on the server.

(Xinhua News Agency June 3, 2009)