Users of the MSN Spaces section of Microsoft Corporation's new China-based web portal get a scolding message each time they input words deemed taboo by the communist authorities - such as democracy, freedom and human rights.
"Prohibited language in text, please delete," the message says.
However, the restrictions appear to apply only to the subject line of such entries. Writing them into the text, with a more innocuous subject heading, seems not to be a problem.
Microsoft staff in China could not be reached immediately for comment.
However, a spokesman at the tech giant's headquarters in Seattle acknowledged that the company was cooperating with the Chinese government to censor its Chinese-language web portal.
Microsoft and its Chinese business partner, government-funded Shanghai Alliance Investment, work with the authorities to omit forbidden words, said Adam Sohn, a global sales and marketing director for MSN.
But he added: "I don't have access to the list at this point so I can't really comment specifically on what's there."
Online tests found that apart from politically sensitive words, obscenities and sexual references also are banned.
MSN Spaces, which offers free web log or blog space, is connected to Microsoft's MSN China portal. The portal was launched on 26 May, and about 5 million blogs have since been created, Microsoft said.
The Chinese government encourages internet use for business and education, but tries to ban access to material or websites deemed subversive.
China encourages internet usage
for business and education
A search on Google for such topics as Taiwan or Tibetan independence, the banned group Falun Gong, the Dalai Lama or the China Democracy Party inevitably leads to a "site cannot be found" message.
Consequences of defying government limits can be severe; 54 people have been jailed for posting essays or other content deemed subversive.
Internet-related companies are obliged to accept such limitations as a condition for doing business in China. And government-installed filtering tools, registration requirements and other surveillance are in place to ensure the rules are enforced.
Recently, the government demanded that website owners register with authorities by 30 June or face fines.
Sohn said heavy government censorship was accepted as part of the regulatory landscape in China, and the world's largest software company thinks its services still can foster expression in the country.
"We're in business in lots of countries. I think every time you go into a market, you are faced with a different regulatory environment and you have to go make a choice as a business," he said.
"We want to make sure that pressure is being put on the companies to pressure the Chinese government to ensure a more democratic process"
Tala Dowlatshahi, spokeswoman for Reporters Without Borders
"Even with the filters, we're helping millions of people communicate, share stories, share photographs and build relationships. For us, that is the key point here."
The international media advocacy group Reporters Without Borders has protested against the online limits, sending letters to top executives of Microsoft, Yahoo!, Google and other companies urging them to lobby Beijing for greater freedom of expression.
"In terms of the reality of the situation, those business deals are going to continue as globalisation expands," said Tala Dowlatshahi, a spokeswoman for the group.
"But we want to make sure that pressure is being put on the companies to pressure the Chinese government to ensure a more democratic process."