China’s internet censorship is well known, but a report has quantified the extent of it, uncovering more than 66,000 rules controlling the content that is available to people using search engines.
The most diligent censor, by at least one measure, is Microsoft’s search engine Bing, the only foreign search engine operating in the country, according to the report, which was released on Wednesday by the Citizen Lab, a cybersecurity research group at the University of Toronto.
The findings suggested that China’s censorship apparatus had become not only more pervasive, but also more subtle. The search engines, including Bing, have created algorithms to “hard censor” searches deemed to be politically sensitive by providing no results or by limiting the results to selected sources, which are usually government agencies or state news organizations that follow the Communist Party’s line.
“You might get no results if it is a very sensitive topic, but if your query is subject to this kind of self-censorship, what happens is you actually appear to get results as normal, but that’s not actually happening,” said Jeffrey Knockel, a senior researcher at Citizen Lab and an author of the report. “You’re getting results only from certain pre-authorized websites.”
The organization’s researchers studied eight online platforms that offer search tools: the search engines Baidu, Sogou and Bing; the social media sites Weibo, Douyin, Bilibili and Baidu Zhidao; and the e-commerce giant Jingdong.
All are subject to extensive legal restrictions that have long censored criminal activity, obscenity, pornography, violence and gore, in addition to virtually any political, ethnic or religious content viewed as threatening to Communist Party rule and social stability.
More recent restrictions have extended to defamation of the country’s heroes or martyrs, illegal surrogacy and misleading or false information about Covid-19 in Beijing.
Each of the companies have created mechanisms to comply with the government’s ever-evolving restrictions.
The report found that Weibo, China’s equivalent of Twitter, restricted search results for the term “Chinese spy balloon” so that only information from official Chinese sources would appear to those seeking to learn about the surveillance airship shot down by the United States in February.
Baidu blocked all results for searches that included the country’s leader, Xi Jinping, President Vladimir V. Putin of Russia and the international warrant for the Russian president’s arrest issued days ahead of Mr. Xi’s visit to Moscow in March.
The report said that the Chinese tech companies had adopted more rules than Bing, one of the few foreign tech platforms allowed in the country, but compared with Baidu, Bing’s rules were broader and affected more search results. They also on average restricted results from more domains.
Caitlin Roulston, a spokeswoman for Microsoft, said the company would look into the findings but had not yet fully analyzed them. “We are reaching out to Citizens Lab directly to get more information so that we can conduct any further investigation needed,” she said.
Microsoft is one of the few foreign technology companies that still operates inside China, and it has acknowledged that to do so required complying with the country’s censorship laws, something other companies, most prominently Google, refused to do.
Conditions in China have often been fraught for Microsoft, with the company’s products facing crackdowns from the authorities. In 2019, Bing itself was blocked temporarily. In 2021, Microsoft shut down LinkedIn in China after seven years in the country, citing regulatory and competitive obstacles.
Mr. Knockel said the study reinforced the argument that foreign tech companies could do little to restrict censorship or other demands from the government. China, for example, has signaled that it will restrict the operations of artificial intelligence in chat bots, which Microsoft has already unveiled for Bing.
“Just simply allowing American tech companies to do business in China isn’t going to solve any of the censorship or larger human rights issues that we would like to be solved in China,” Mr. Knockel said.