China’s government has launched a counteroffensive against a spate of politically sensitive rumors online. Over the weekend, Beijing authorities arrested six people and shuttered 16 websites for “fabricating or disseminating online rumors.” And, in an unprecedented move, China’s Twitter-like microblogs shut down their comment sections entirely.

The clampdown is likely a delayed response to online discussion last month that swirled around the ouster of rising political star Bo Xilai, including pernicious rumors of of a coup attempt in Beijing.

“Recently, individuals on the Internet, particularly on microblogs, fabricated and spread the so-called ‘military vehicles have entered Beijing, something has happened in Beijing’ rumors, which has caused an adverse social impact,” Xinhua, China’s state-run news service said in announcing the move.

Chinese microblogs, known as weibos (literally: “microblog”) went wild with commentary last month after Bo was dismissed from his job as party chief of Chongqing, a city of 30 million in China’s southwest. The son of a Maoist father, Bo was the politically ambitious poster boy for China’s hardline left, making him enemies among China’s more pragmatic and cautious political establishment.

Weibos similarly broke news last month after Bo’s former right-hand man, Wang Lijun, was reportedly denied political asylum at the U.S. consulate in Chengdu. Wang was arrested outside the consulate and subsequently disappeared into the state security apparatus. The official cause of his departure was “stress.”

But those events happened more than a week ago. What took the censors so long to act? As Time’s Austin Ramzy noted, China largely relies on Internet companies to censor themselves. “In a quickly changing situation, the reaction of cautious officials can be to do nothing,” Ramzy wrote at Time’s Global Spin blog. “As a result, it can take time before propaganda authorities and the Internet outlets they regulate clamp down on sensitive discussions.”

The Weibo shutdown isn’t permanent. Sina Weibo and Tencent, China’s two largest microblogging services, will reopen their comment sections on April 3, after shutting them down on March 31.

“Recently, rumors and other illegal and harmful information spread through microblogs have had a negative social impact, and harmful information has been relatively predominant in comment sections, requiring concentrated cleansing,” Sina Weibo wrote in announcing the clampdown.

It’s hardly a surprise the companies resorted to such a drastic move. Chinese netizens have shown time and again that all it takes to avoid “concentrated cleansing” is some creative vocabulary usage. The fact that Weibo needed to shut down comments entirely shows that in China’s cat and mouse game of Internet censorship, the mice just may be winning.

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