Software giants Microsoft, Google and Yahoo! have been collaborating with the Chinese authorities to curtail freedom of expression and suppress dissent against their proclaimed values, Amnesty International said.

"All three companies have, in one way or another, facilitated or colluded in the practice of censorship in China," said the rights organisation, which released its report on China titled "Undermining freedom of expression in China - the role of Yahoo!, Microsoft and Google terror", here Thursday.

"Yahoo! has provided the Chinese authorities with private and confidential information about its users. This included personal data that has been used to convict at least two journalists, considered by Amnesty International to be prisoners of conscience," the report said.

It pointed out that Microsoft had admitted to shutting down a blog on the basis of a government request. "Google has launched a censored version of its international search engine in China.

"All three companies have demonstrated a disregard for their own internally driven and proclaimed policies," the Amnesty alleged.

It has criticised Yahoo! more harshly. "Yahoo!'s actions have, in particular, assisted the suppression of dissent with severe consequences for those affected. The company allowed its Chinese partner to pass evidence to the authorities that was subsequently used to convict individuals, at least two of whom received long prison sentences for peacefully exercising their legitimated right of freedom of expression."

The rights group said the Internet companies had justified their action by an argument that they were under an obligation to comply with the local law.

"They argue that although it is not an ideal situation, their presence in China is a force for good. They assert that without their input, censorship would still take place and that censored information is better than no information at all."

Amnesty alleged that instead of bringing changes in Beijing, where these Internet companies were present for more than a decade, they were "attempting to gain an increasing share of a rapidly growing market of knowledge".

"In effect, their activities are facilitating and sanctioning government censorship rather than challenging it."

The rights group urged the Internet companies to publicly commit to honouring the freedom of expression and be transparent about the filtering process used by the company in China and around the world.

Amnesty also called on the companies to develop an explicit human rights policy, clarify to what extent human rights considerations are taken into account in the processes and procedures that the company undertakes and exercise leadership in promoting human rights in China through lobbying.