SEOUL, July 8 (Xinhua) -- Distributed denial-of-service (DDoS) attacks that struck a number of South Korean websites late Wednesday, including the presidential office Cheong Wa Dae's, have been confirmed to originate from some of the zombie computers infected in massive attacks a year ago, police said Thursday.
"We found yesterday's DDoS attacks traced to zombie computers that were used in last year's attacks and left untreated, which became active at the same hour and same day after lying dormant for a year," the Cyber Terror Response Center of the National Police Agency said Thursday.
Zombie computers are computers that have been secretly compromised by hacking tools which allow a third party to be in control of them.
These computers are assumed to be programmed to resume the attacks on 25 designated websites in South Korea and the United States on July 7 every year, the center said.
The police said that a mere 462 zombie computers were used in the latest attacks, compared with 270,000 last year.
The possibility of another round of attacks is high, according to the police.
The state-run Korean Communications Commission (KCC) said Wednesday that the websites of government agencies, such as the presidential office Cheong Wa Dae, the Ministry of Foreign Affairs and Trade, and private firms, including the leading internet search engine Naver, Nonghyup Bank and the Korean Exchange Bank, were hit by the so-called distributed denial-of-service (DDoS) attacks from around 6 p.m. (0900 GMT) Wednesday.
The attacks came just one year after a large-scale DDoS attack shut down 25 internet sites for days.
But the KCC said the latest attacks are "at a very low level" compared with what occurred last year, and posed no major threat.