Thousands of censors delete China's tweets

Posted by Emma Woollacott

Chinese censors work very, very quickly, it seems, with a new report concluding that they're getting rid of unwanted posts on local Twitter clone Weibo almost immediately.

A team headed by Dan Wallach at Rice University examined the posts of around 3,500 users whose posts had been removed in the past. And, they found, around 12 percent of messages were removed over a 15-day monitoring period - more than 4,500 per day. And of these, most were removed very quickly.

"We found that deletions happen most heavily in the first hour after a post has been submitted," write the researchers.

"Focusing on original posts, not reposts/retweets, we observed that nearly 30 percent of the total deletion events occur within 5-30 minutes. Nearly 90 percent of the deletions happen within the first 24 hours."

It's no surprise which topics get their authors' posts wiped: "Using Independent Component Analysis, we find that the topics where mass removal happens the fastest are those that combine events that are hot topics in Weibo as a whole (e.g., the Beijing rainstorms or a sex scandal) with themes common to sensitive posts (e.g., Beijing, government, China, and policeman)," says the team.

But how is the Chinese government working so fast? Presumably, say the researchers, by hiring a lot of people.

"Suppose an efficient worker can read 50 posts per minute, including the reposts and figures included in the posts," they say.

"Then to read Weibo’s full 70,000 new posts in one minute, 1,400 workers working at the same time would be needed. If these workers only worked in 8 hour shifts, 4,200 workers would then be required."

Some of this work is probably handled by automated systems, looking for keywords - although this is much harder in Chinese, because of the complexity of the language and the way abbreviations are routinely used on Weibo.

An analysis last year from Carnegie-Mellon University found that particular words were a sure-fire way to censorship - Falun Gong, for example, or certain ordinary words used as euphemisms for sex or political activity. The team concluded that key-word recognition must be involved.

But, says the Rice team, there's plenty of evidence that human beings are also censoring Weibo, probably checking posts highlighted by the automatic systems. Most notably, the frequency of deleted posts drops noticeably when the national TV news comes on. Even censors like to get some information now and then...