Many government and corporate sites in the hi-tech Baltic nation have been crippled for almost three weeks after being flooded with enormous amounts of traffic.

Prime Minister Andrus Ansip had claimed that some of the cyber-attacks, which forced the authorities in the tiny Baltic state to temporarily shut down Web sites, came from Russian government computers, including the president's office.

But Tallinn has now backed away from such explicit accusations. Estonia's defence minister Jaak Aaviksoo said there was a possibility of Russian involvement in the attacks that involved at least one million computers.

The Kremlin has dismissed the accusations, saying hackers could have used a false IP address to tarnish the Russian authorities.

Coincidence?

The start of the cyber-attacks coincide with the start of a row with the Kremlin over the removal from central Talinn of a post-World War II memorial to Soviet Red Army soldiers.

The NATO spokesman remained vague on the question of Russian involvement. "It's not that easy because of the nature of cyber space," he said. He added that "various indications" had been identified.

But he said that tracking and identifying the cyber attackers was not the primary goal of the investigations. "Our aim ultimately is protection."

He told AFP, "We do see it as serious because it was concerted. It's clearly not the sort of thing that two teenagers, for whatever their motives, do. We are talking about a pretty well-organised thing."

"This is a special case because of the scale of this attack. So of course allies are going to help and we are not just treating this as an Estonian problem, of course it is a problem for NATO," the spokesman added.

Growing threat

At present, NATO does not define cyber attacks as clear military action. This means the provisions of collective self-defence would not apply to the attacked country.

US Deputy Secretary of State John Negroponte told a number of leading European newspapers on Friday that cyber attacks were likely to become more of an issue in the future.

A common method of achieving such attacks is by hijacking computers belonging to normal web surfers using a virus or other malware picked up from an infected e-mail attachment or by visiting a website that hosts such malware.

Estonia, which has a large Russia minority, is a pioneer in the development of e-government and a very wired society. This also makes it very vulnerable to cyber attacks.