Terms related to political activists, anti-government movements and state censorship efforts are the most likely to be censored on Chinese blogs and social media sites, according to researchers at Carnegie Mellon University.
The "Chinese Firewall" is known to blocks certain websites - including parts of Google and Facebook - but the CMU study is one of the first to examine individual messages, words and terms that have been censored.
Researchers found that the names Ai Weiwei and Liu Xiaobo, two Chinese political protesters, as well as the term Linagui, which is a code term for planned protests, are blocked on Chinese websites and microblogs called weibos at high rates.
Researchers studied 57 million messages posted on Sina Weibo, which is a Chinese microblogging site akin to Facebook or Twitter with 200 million users. Researchers used the site's API to find terms that had been deleted.
During a two-day period in July, 93 of 114 messages on Sina Weibo containing the name of Tiananmen Square protester Jian Zemin, who was rumored to have died, were deleted. Researchers also found that politically sensitive terms, such as the name of Fang Binying, one of the reported architects of the Chinese Firewall, is likely to be blocked, as was a term meaning "to ask someone to resign," especially after a deadly high-speed rail crash last year.
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Even less innocuous terms were found to be censored, including words meaning iodized salt and radioactive iodine, which researchers found had high delete rates after the Japanese earthquake when there were some fears of salt contamination.
The study also found that some geographic areas had high levels of censorship compared to others. In Tibet, for example, which has been fighting for political freedom from the Chinese government, more than half of the posts originating from the area were deleted.
Other terms subject to deletion included spam and pornography, which are blocked on certain websites in the United States as well.