The Guardian reported yesterday that Microsoft's search engine Bing appeared to be censoring information for Chinese-language users in the United States as it would censor results in mainland China. Microsoft has denied the allegations, blaming the exclusion on a technical error.

The claim that Bing censors Chinese-language searches in the US was first made by censorship blog Greatfire. The author of the blog, Charlie Smith, said he found the differences while searching for FreeWeibo.com, a site that allows anonymous searching of Chinese social networks and blogs. Smith told The Guardian that FreeWeibo's homepage — which did appear on Google — would not appear on Bing. Further research apparently showed that Bing users searching for controversial China-related topics, including the Dalai Lama, the Tiananmen Square protests of 1989, and the Falun Gong movement, found "radically different results in the US for English and Chinese language searches."

Stefan Weitz, senior director of Bing, denied the claims that Microsoft is censoring information outside of China. He explained in a statement sent to The Verge that the absence of FreeWeibo's homepage in its searches was "due to an error in [Bing's] system," and the homepage had been "at some point in the past marked as inappropriate due to low quality or adult content." Weitz said his team had now conducted a review, and deemed the page "acceptable for inclusion in global results."

Weitz said that Bing "does not apply China's legal requirements to searches conducted outside of China." Sources familiar with the matter told The Verge that Microsoft only applies the kind of censorship Chinese law still demands to IP addresses originating from inside China, and said those who set their location to the country would not trigger any filters or be shown censored search results. The same sources suggested FreeWeibo's homepage would be restored to Bing's search function soon.

But in addition to the exclusion of FreeWeibo, The Guardian also claimed that Chinese-language searches for a range of controversial China-related topics produced unexpected results. The British publication found that an English-language Bing search for the Dalai Lama would return his official website, followed by links to his Wikipedia, Facebook, and Twitter pages. A Chinese-language Bing search conducted outside of China would first return a documentary made by Chinese state broadcaster CCTV, followed by entries from Baidu Baike, China's "heavily censored Wikipedia rival." Google, The Guardian says, generates "broadly similar results" for the same search in the two languages. Microsoft did not respond directly to these wider allegations of censorship, but it should be noted that searching both Google and Bing using different alphabets and languages will sometimes produce varied results.

Update: Microsoft has published an official response.