HONG KONG—China's 47 million bloggers are frequently subjected to censorship by their Internet service providers, but politically sensitive material also routinely falls through the cracks as individual companies interpret government guidelines in their own way, a new report shows.

In the first in-depth report to focus on user-generated content on social media and blogging platforms, researchers found that censorship levels across 15 different Chinese blogging platforms varied even more than expected.

The report, titled "China's Censorship 2.0: How Chinese Companies Censor Bloggers," also says "a great deal of politically sensitive material survives in the Chinese blogosphere, and chances for survival can likely be improved with knowledge and strategy."

China had 253 million Internet users by mid-2008, according to official statistics from the China Internet Network Information Center.

They spend more time online than netizens in any other country with the exception of France and South Korea.

Chinese Web surfers are also more likely to contribute to blogs, forums, chat rooms, and other social media like photo and video-sharing sites.

Methods vary

According to study lead author Rebecca MacKinnon of the University of Hong Kong, while the government lays down strict censorship guidelines for Internet companies to follow, censorship methods vary greatly from company to company.

"Companies do have at least some ability to make strategic choices," MacKinnon wrote in her report, published in the online journal First Monday.

"These choices are not only about how to balance relationships with government and users, but also about the extent to which [companies] value user rights and interests."

Previous studies of Chinese Internet censorship have focused on filtering, an automated method that uses lists of banned or sensitive keywords such "Tibetan independence" to prevent users from accessing Web sites at all.

A study by the Open Net Initiative in 2005 found China's Internet filtering system to be "the most sophisticated in the world."

Flawed firewall

But MacKinnon said the filtering system, known as the "Great Firewall," is imperfect because it can be circumvented by more technologically savvy users.

"Censorship of Chinese user–generated content is highly decentralized," writes MacKinnon, who is also a co-founder of the seminal blogging platform Global Voices.

"Implementation is left to the Web companies themselves."

Some Chinese Web companies who censored in an inefficient way were still able to stay in business, the report said, leaving "a substantial amount of politically critical content" still available in China's blogosphere.

MacKinnon's researchers found that not a single content item was censored by all 15 blogging platforms.

Even a test news item they posted about the banned spiritual movement Falun Gong was censored by only 13 companies; this was the highest number of service providers to censor the same item.

An item posted across all 15 platforms on Tibetan independence was censored by just 12 of them, while an excerpt from the Dalai Lama's open letter to the Chinese people and an item about the "Tiananmen mothers" Web site, for those who lost relatives in the 1989 military crackdown, were both censored by only nine companies.

Items already reported by domestic media were censored even less, while political satire and humor were allowed the longest leash of all, the study found.

Overall, posts related to Falun Gong, the 1989 Tiananmen crackdown, and Tibet independence were the most heavily censored, as expected.

Posts mentioning "sudden incidents," the Olympics, and corruption were also highly likely to be deleted.

Censorship methods varied from deleting entire posts with no explanation, to replacing offending posts with an apology note, to hiding posts from public view, to replacing forbidden words with asterisks while leaving the rest of the text on view.

Reported by Luisetta Mudie. Edited and produced for the Web by Sarah Jackson-Han.