There is cyber-dissident Li Zhi, a former civil servant who was given an eight-year prison sentence for subversion for writing essays critical of the government.

There is Jiang Lijun, sentenced to four years in prison in 2003 for writing a series of pro-democracy articles. The most recent case is Wang Xiaoning, sentenced to 10 years in prison in 2003 after sending from his Yahoo e-mail account articles that called China an 'authoritarian dictatorship' and urging free elections.

In each of the cases, mainland officials were able to pursue their cases in part because they had assistance from Yahoo, which turned over details about its users' e-mail accounts. The company's response to date has been that it regrets the actions, but must comply with the laws of the country where it operates.

This is true of any foreign company doing business in China, and Yahoo is not the only United States firm that has failed to uphold democratic values.

Other companies to come under criticism include Microsoft, which censors words such as 'freedom' and 'democracy' from its blogging service; Google, which censors search results at its Google.cn service; Cisco Systems, which reportedly has instructed Chinese officials on how to censor the internet; and Skype Technologies (owned by eBay), which filters out sensitive words during instant text messaging conversations.

But Yahoo should be singled out for criticism because its actions have led to the loss of liberty of four people, who arguably had higher expectations that the American company would protect their information.

In addition to Congressional hearings in the United States, Hong Kong's Privacy Commission has launched an investigation into whether information provided by Yahoo Holdings (Hong Kong) - cited in many related court documents - led to the imprisonment of Shi Tao.

What makes Yahoo different from its counterparts is its decision to locate servers within China's borders, which puts it under mainland legal jurisdiction. When faced with a government demand for information, Yahoo risks its employees being imprisoned if it refuses to comply.

Not surprisingly, human rights groups such as Reporters Without Borders have called on Yahoo to remove its servers from the mainland to keep sensitive user information from the government's reach.

'Chinese journalists and dissidents used to trust Yahoo more than local companies to protect the confidentiality of their electronic communications,' the group said.

'This company has betrayed them by shamefully collaborating with the police. It has said that it is 'distressed' by the situation, but the time for lamentation is past.

'We expect Yahoo executives, particularly [co-founder] Jerry Yang, to announce that they will withdraw their e-mail servers from China.'

Whether such a move would help remains uncertain. Yahoo has transferred its China business to the mainland's Alibaba.com as part of its US$1 billion investment in that company. Alibaba chairman Jack Ma had said he would have co-operated with authorities if confronted with the same decision.

The American internet firms argue their presence in the mainland will have a beneficial effect, and to an extent this is true. Although Skype filters sensitive words from text conversations - just as mainland operator Tencent Holdings does for its QQ programme - it also provides encrypted voice calls. Dissidents who are unable to type about Tibetan independence can simply place a voice call instead.

Google's English-language search service was popular on the mainland and a serious rival to domestic player Baidu.com long before it launched the censored version, Google.cn.

One might argue that these trade-offs are acceptable because there exists alternative means for Chinese users to access information over the internet. But the imprisonment of four people is not a trade-off we should accept.

Yahoo should make amends, starting by offering some of its US$2.43 billion in cash holdings to compensate the families of the victims. The company should then reorganise its mainland business to ensure that no others lose their freedom as a result of its actions.