SEOUL, Korea - Seoul's spy agency has yet to be sure that North Koreans were behind recent cyber attacks on South Korea and the United States but it still sees Pyongyang as a prime suspect, officials said Sunday.

The National Intelligence Service (NIS) said in a statement it was still looking into 'various pieces of evidence' indicating that North Koreans might have orchestrated the attacks against South Korean and US government and private websites.

"The NIS... has yet to reach a final conclusion that the acts have been committed by North Korea," the statement said.

It denied a report by Chosun Ilbo newspaper on Saturday that the NIS had found an Internet protocol (IP) address used by a North Korean hacker surnamed Yun, who could be behind the cyber attacks.

It said the Chosun Ilbo report went "too far" and urged local media outlets to be prudent in reporting on the case.

Hackers have planted viruses in thousands of personal computers in South Korea, one of the world's most wired societies, as well as overseas.

These mounted "distributed denial of service" (DDoS) attacks designed to seek simultaneous access to selected sites and swamp them with traffic.

The Korea Communications Commission in Seoul said Sunday more than 690 personal computers had been damaged in the cyber raid.

The attacks that had crippled some South Korean government websites have now come under control after virus-infected "botnet" hosting servers were isolated and "vaccine" programmes were widely distributed to PC users.

The North has staged a nuclear test and numerous missile launches in recent weeks, raising regional tensions.

But a cyber attack, if confirmed, would be a new tactic.

Seoul's Yonhap news agency said the NIS on Friday told lawmakers in a closed-door briefing that a North Korean research centre called "Number 110" seems to have orchestrated the attacks.

The General Staff of the People's Army in North Korea runs the research centre which is a "well-trained unit on cyber attacks", according to Yonhap.

The agency said Sunday, quoting an unnamed intelligence source, that North Korea had stolen personal data on at least 1.65 million South Koreans through hacking into various websites since 2004.

The North mainly targeted the websites of retired military officials, security-related centres and university alumni associations, it said.

The NIS said Friday the cyber raid was tracked to 86 Internet protocol addresses in 16 different countries, including the United States, Japan, China and Guatemala ? but not North Korea.