Weibo (officially Sina Weibo) is a popular, self-censoring Chinese micro-blogging website. Established by the Sina Corporation in 2009, Weibo functions a hybrid of Facebook and Twitter. Weibo is particularly popular among celebrities among diverse parts of the globe while business companies see it as an innovative approach to reach out to their Asian consumers. Though Weibo has achieved numerous successes in China, ethical complications in censorship hinders its ability to project freedom of speech, unlike it's American counterparts.
Background and Features
The name, Weibo, derives from the Chinese portmanteau for "microblogging". In the beginning, Weibo invited many celebrities to join the microblogging website. Weibo censors certain keywords that its developers deem sensitive or "rumorous". The developers are constantly sharpening Weibo's governing mechanisms in order to squash undesired topics through a variety of channels. For this reason, it is endorsed by the Chinese government as a social networking platform.
Users are limited to posting 140-character status updates. They may also share photos, videos, or audio clips along with these updates. Posts may be "forwarded", the equivalent of Twitter's "retweeting".
Recently, many celebrities and famous individuals have recognized the social power of Weibo. For example, Coco Rocha is a famous high fashion model who signed up for a Weibo account. In a little over two months, Rocha has 100,000 "friends" or followers. Business magnate Bill Gates as well as actor-producer Tom Cruise both have verified Weibo accounts. 
Many individuals and companies are now realizing how lucrative the Chinese Market can be for their products and brand images. Many are signing up for Weibo as a way to reach out to their Chinese consumers, fans and supporters.
Currently, the site boasts membership in the 100 millions. Sina Weibo plans to launch an English version of the site by the end of 2012 while Twitter plans on releasing a Chinese version as well. This will be its second endeavor, and Twitter hopes that it will be a competitive success against Weibo. It is not expected to succeed due to the complexity of China's censorship laws. Twitter did not originally have a very significant Chinese usership even before the Chinese government decided to block Twitter the first time on June 2, 2009 .
Notable Incidences of Weibo Censorship
Wenzhou Train Collision
On July 23, 2011, two CRH trains collided in the city of Wenzhou, Zhejiang Province. The crash killed 40 people and injured 191. News of the accident circulated immediately through Sina Weibo, with the original post "retweeted" over 100,000 times within ten hours. The Chinese government response to the crash as well as rescue operations were handled poorly, causing "Railway Ministry" to rise to #1 trending hashtag on Weibo where it remained for days until it was removed by the website administration in an act of auto-censorship.
The government attempted to perform damage repair by declaring a media blackout on the incident throughout the country, but videos of the crash site were already going viral on the internet.
"All articles on the Wenzhou train collision are to be put off the homepage with immediate effect. None are to be put on the homepage itself. In the news section, only one article may be placed there, but no commentaries are allowed. Promoting the discussion of related topics on forums, blogs and microblogs are not allowed."
- — Chinese government mandate to media outlets, translated by The Shanghaiist
Weibo users persistently tried to keep the topic alive, some posts even directly implored "Conscientious moderators don't delete this post" 
Censoring the Occupy Movement
In October 2011, reacting to the Occupy protests throughout the United States, Sina Weibo began to censor the Chinese word for 'occupy' in conjunction with various place names in China.  Although the Occupy movement has yet to become a topic of discussion among Chinese netizens, the government has begun filtering keywords in order to preemptively stop the idea from potential circulation.
One reason why Weibo is so popular in China is because it is supported by the Chinese government. The Chinese government has direct control over its content, unlike other social networking sites like Facebook and Twitter that have servers located across the world. The fact that Weibo has the Chinese government overseeing its content leads to the debates having to do with censorship, particularly whether such censoring of user-generated content is morally and ethically correct. There is no right to free speech on this site, which is particularly concerning since you don't really have to ever leave it to get the content you want - micro-blogging, videos, commerce, games, and viewing other online content without ever leaving the site.
Despite having the Chinese government having direct control over its content, Weibo itself, is still simply a relatively free stage for sharing information. All the comments expressed on this online stage and even the underlying principles that they expose, are closely tied to the common understanding of the entire society. If Weibo has a ethical line, then this line should be drawn by its users collectively.
Similar Censorship in the United States
In light of the recent Occupy movement around the U.S., incidences of large social media websites censoring sensitive material and keywords pertaining to the movement have also sprung up. Several journalists' Twitter accounts were suspended on grounds of constant coverage of Occupy Wall Street. 
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