The master computer which controlled last week’s massive cyber attack on websites in the US and South Korea is in Britain, Asian computer security investigators claim.

The attack, which paralysed the websites of South Korean and United States government agencies, banks and businesses over the course of a week, was first blamed on communist North Korea. But having traced the attack back via proxy computers used in the attack, a security company in Vietnam has identified a server belonging to Global Digital Broadcast, a Brighton-based internet television company as the source of the attacks.

The analysis, by a Vietnamese company, Bach Khoa Internetwork Security (BKIS), was carried out at the request of the South Korean government. Yesterday, South Korea emphasised that it was not clear whether Global Digital Broadcast was the origin of the attacks or whether it was also being manipulated by a master computer.

"The [Brighton] server appears to have controlled compromised handler servers,” Park Cheol Soon of South Korea’s communications commission. told Agence France Presse. “However, it needs more investigation to confirm whether this server was the final attacker server or not.”

Global Digital Broadcast wrote on its website that it was aware of the issue and had “treated it with utmost severity” but had “discounted it as coming from a North Korean Government site” suggesting the source of the attack was based in America.

A Serious Organised Crime Agency spokesman said: “We are involved, and are aware from the information and are assisting with the information.

“We have spoken to the company involved. But this this is not our investigation, we’re just dealing with the company on the UK side.”

The attack was the kind known as distributed denial of service (DDoS) which uses a malicious computer virus to instruct infected computers, causing them to flood the targeted websites with traffic. The simultaneous accessing by so many users overloaded the web servers, causing them to shut down.

Estimates of the number of “zombies”, or infected computers, used in the attack have varied from 20,000 to 50,000. But BKIS claims to have counted 166,908 zombies from 74 countries around the world that have been used for the attacks, including China, Japan, Canada and Australia.

South Korea’s intelligence agency reported that the cyber attacks were fizzling out early this week. At their height, they temporarily shut down the websites of South Korea’s president, the country’s National Assembly, the defence and foreign ministries, the ruling party, a newspaper, two banks and the US-South Korea combined forces military command. The attacks appear to have affected only external public websites.

South Korean intelligence officials told MPs that they suspected North Korea was behind the attacks, but this has not yet been proved. Mr Park said that the information about the British computer did not settle the matter one way or the other. “It does not either bolster or undermine claims that someone [in particular] has done the attacks,” he said.

Although nothing on this scale has been reported in South Korea before, the prime minister, Han Seung Soo, has spoken of the danger of cyber-espionage by Chinese and North Korean hackers. The country’s Defence Security Command said last month that it was logging attempts to penetrate military networks at an average rate of 95,000 a day.

Estonia accused Russia of launching a similar cyber-attack on it in 2007. Two years earlier, Japanese businesses and government websites were temporarily shut down by Chinese hackers, during a row over the Japanese prime minister’s visits to a nationalist war shrine. Last September, websites run by exiled Burmese dissidents faced similar assault – the suspicion then was that it was done at the instigation of the dictatorship which they publicly revile.