BEIJING - GOVERNMENT computers in France have been the target of hackers linked to China, claims a top French official, following allegations that they have also infiltrated systems in Germany, Britain and the United States.

But China's Foreign Ministry yesterday refused to respond to the comments by Mr Francis Delon, Secretary-General of French National Defence, although a spokesman for the ministry had said last week that such accusations were 'groundless' and 'a result of ulterior motives'.

Mr Delon said last Saturday that information systems in France had been infiltrated by groups involving China, although he did not directly implicate the Chinese military as unnamed officials in other countries have done.

'We have indications that our information systems were the object of attacks, like in the other countries,' he said, confirming a report published in French newspaper Le Monde.

'We have proof that there is involvement with China. But I am prudent. When I say China, this does not mean the Chinese government. We don't have any indication now that it was done by the Chinese People's Liberation Army.'

Two weeks ago, Germany's Chancellor Angela Merkel warned at a joint news conference with Chinese Premier Wen Jiabao in Beijing that the two countries should observe 'a set of game rules', referring to reports that hackers linked to the Chinese military had attacked computers in her Berlin office and other German government departments.

Mr Wen did not dispute the reported hacking but attempted to distance his government from the accusations and promised to cooperate with global efforts to combat computer crime.

Since then, there have been other reports that Chinese hackers had attacked government units in Britain.

The Pentagon said last week that US military computers had been penetrated earlier this year, but declined to comment on a report in the Financial Times that the Chinese military was behind the hacking.

Critics say possible motives for the hacking range from the stealing of secrets or confidential technology to probing for system weaknesses and placing hidden viruses that could be activated in a conflict.

But experts say responsibility for the attacks is not conclusive, pointing out that China is home to many insecure computers and networks that hackers in other countries could use to disguise their locations and launch hits.

'It is often difficult to pinpoint the true origin of an intrusion into computer systems and even more difficult to tie the intrusion to a specific nation or government,' Pentagon spokesman Bryan Whitman said.

In journals and military publications, Chinese defence analysts have noted that computers are a crucial link in military command, control and intelligence networks.

Computers relay communications, control guidance and navigation systems and even form the backbone of complex logistics systems supplying food, fuel and ammunition to military forces.

These networks are even more important to militaries like that of the US, with bases and facilities spread all over the globe.

In a conflict, attacking these systems with viruses, false information or intelligence-gathering software could partially offset the considerable US advantage in technology and firepower, Chinese analysts say.

Some foreign analysts suspect that it is difficult for the civilian leadership to keep track of cyber warfare research and development because it is not centralised under a single military or intelligence command.

Whether or not cyber attacks are officially approved, China has become a growing focus of global anti- hacking efforts, partly due to the size of the country's Internet user population, now estimated at 140 million.

In a report earlier this year, security software maker Symantec Corp listed China as having the world's second-largest volume of malicious computer activity, after the US.

Experts say attacks originating in China often employ standard weaponry such as Trojan horses and worms, but in more sophisticated ways. In some cases, hackers slip in after launching viruses to distract monitors, or coordinate multiple attacks for maximum effect.

ASSOCIATED PRESS, INTERNATIONAL HERALD TRIBUNE, AGENCE FRANCE-PRESSE