Government attempts to censor Internet sites are useless because people can still use e-mail or other means to spread banned information, Microsoft founder and chairman Bill Gates said.

"The ability to really withhold information no longer exists," he told a news conference in Lisbon as part of a Microsoft-sponsored forum.

"You may be able to take a very visible Web site and say that something shouldn't be there, but if there is a desire by the population to know something, it is going to get out," he added.

Human rights groups have blasted Microsoft, the world's largest software company, and key Internet players Yahoo and Google for giving in to China's restrictions of free speech.

Last year Microsoft shut down the site of a popular Chinese blog, a journal accessible on the internet, at the request of Beijing authorities.

Earlier this month online search engine leader Google agreed to censor its search results in China, which has the internet's fastest growing market.

Cisco is also accused of helping the government track cyber-dissidents.

Meanwhile, US politicians and rights groups have condemned Google, Microsoft, Cisco, and Yahoo for collaborating with China to censor the Internet.

In a briefing by the Congressional Human Rights Caucus, the four US companies were accused yesterday of putting profits before principles in their push into the Chinese market.

"They should not let profits take precedence over traditional democratic values such as freedom of speech," said representative Tim Ryan, who led the briefing.

"With all their power and influence, wealth and high visibility, they neglected to commit to the kind of positive action that human rights activists in China take every day," representative Tom Lantos said of the companies.

"They caved in to Beijing's demands for the sake of profits," Lantos said.

The four companies refused invitations to take part in the briefing.

Instead, in a joint statement, Microsoft and Yahoo suggested they wanted the US government to help solve the Chinese censorship problem.

"We urge the United States government to take a leadership role in this regard and have initiated a dialogue with relevant US officials to encourage such government-to-government engagement," the two companies said.

"We want to assure members of Congressional Human Rights Caucus and the public at large that we do not consider the internet situation in China to be one of 'business-as usual'," they said, adding that they were seeking better ways to protect the interests of users of their services.

The four companies have been summoned to a February 15 hearing by the House International Relations Subcommittee, which oversees human rights issues.

Anti-censorship groups Reporters Without Borders, Amnesty International and Human Rights Watch said they supported having Congress push the companies to put in place a uniform code of conduct which will protect freedom of speech.