GreatFire.org said its research showed that Microsoft's Bing search engine was filtering out search results on sensitive subjects like the Dalai Lama — when his title was entered into Bing in Chinese characters — whether users were in China or abroad.
"Our latest research indicates that Microsoft's search engine Bing is censoring English and Chinese language search on its home page in order to exclude certain results," the group said. "We have also noticed that Bing is practicing subtle censorship with search results. In both instances, Bing is filtering out links and stories that the Chinese authorities would deem damaging."
The organisation also accused Bing of a lack of transparency by not always notifying users that some search results had been censored, as is normal practice.
Microsoft denied the charges, blaming a system fault rather than a deliberate policy.
"Due to an error in our system, we triggered an incorrect results removal notification for some searches noted in the report but the results themselves are and were unaltered outside of China," Stefan Weitz, senior director for Bing, said in a statement e-mailed to the Reuters news agency Wednesday.
Even outside China, a search for the "Dalai Lama" in Chinese on Bing omitted several Web sites that showed up on Google, appearing to prioritize Web sites sanctioned by the Chinese government over those run by exile supporters of the Tibetan religious leader. The English-language search engine results on Bing did not appear to have been censored and were similar to Google's results.
Microsoft has come under fire in the past for censoring the Chinese version of Internet phone and messaging software Skype, Reuters noted, adding that the company has made no secret of its aim to build a bigger presence in the country.
GreatFire.org said its own Web site, freeweibo.com, appeared to have been subjected to particularly heavy censorship on Bing, with its index page not appearing on searches carried in English or Chinese. Freeweibo collects and preserves microblog posts which have been censored and deleted by the Chinese authorities.
China carries out active censorship of the Internet to prevent dissent and social unrest threatening Communist Party rule. All Internet firms operating within China comply with the government's requirements.