Is the Great Firewall blocking outgoing traffic only?

Connection reset. That is the famous response shown to web users in China when they are trying to access one of the over 2600 websites and searches that have been blocked by the authorities. But what is actually blocked and what is causing the connection disruption? Our research suggests that the Great Firewall (GFW) does not filter any incoming data, but only the outgoing traffic.

It is often said that the GFW imposes three types of censorship. The first one is DNS poisoning. For example, this happens when users in China attempt to access The name servers return an incorrect IP address which doesn't work. The browser tries to load the website for a certain period of time until the whole exercise 'times out'.

The second type of censorship is keyword-based. For example, if one tries to search on Google for facebook, freedom  or some of the other 250+ blocked searches, the connection is immediately reset. In addition, users are restricted from accessing any content on the same website for a minute or so.

The third type is supposed to be content based. Regardless of what was searched for or the address that was entered, if the content contains certain keywords, it is supposed to be blocked. This is where our findings become relevant. They suggest that the GFW doesn't interfere at all with the content that is sent back to the web user in China.

One way to illustrate this is to look at some sample blocked keywords, such as those listed in the table found in the top right on this page. The first example is facebook. is blocked in China, and so is the keyword facebook. This means that if you try to search in Google for facebook, your connection will be reset. The first result of that page is of course But if we search for a slightly different keyword - face book - the connection is not reset. The result is the same though - we still find

The error message displayed in China when trying to access blocked content.

The second example is the keyword . Why this keyword is blocked is a bit of a mystery - 王, or Wang, is one of the most common surnames in China. One possible explanation is 王府井, or Wangfujing, which is the main shopping street in Beijing and also the chosen location for the attempted Jasmine protests earlier this year. Another explanation is that Wang is bound to be the surname of many dissidents in China, purely because the name is so commonplace. Regardless, the first Google result when searching for 王 is the Wiktionary page for the word. Can we use another way to find the same result? We could enter the complex search term wiktionary wang "han character" and we would find the same Wiktionary page. Except in this instance the connection is not reset.

The third example is the keyword freedom, also blocked in China. One of the first results is the Wikipedia page for freedom. Again, if we alter the search slightly, and instead look for wikipedia free dom, the search is not blocked.

What does this all mean? For one, you could set up mirrors of blocked websites and, as long as they don't contain blocked keywords in the URLs or other data being sent to the server, they should be able to jump the GFW. An example of this could be Wikileaks. Their main website is blocked in China, but they have a large number of mirror websites, and our system currently contains three such mirror websites none of which are blocked (,,

Also, any GFW circumvention tool could focus solely on encrypting outgoing traffic, and returning all responses unmodified.

Do you have any findings suggesting otherwise? Please add your comments below!


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Wed, Mar 19, 2014

Bing Bests Baidu Censorship


Independent research from Xia Chu has shown that, in addition to non-China content, Bing censors a vast amount of content that is hosted inside China and which is not censored by China-based internet companies like Baidu. After communicating our issues with Microsoft, Bing removed certain censorship rules (kudos to Bing), but much work remains to be done.

We recently called for Microsoft to release its transparency report for Bing (as have others - full disclosure, Rebecca sits on our advisory board).  Microsoft has yet to respond to this request. But Xia’s independent research of Bing’s China censorship policy could be regarded as a de facto transparency report for the search engine.

In this thorough study, the results of which we have verified, Xia examined Bing's SERP (search engine results page) for over 30,000 sensitive and nonsensitive query terms, and launched these queries from both inside and outside of China. Comparing and examining these results, plus querying with special search operators, reveals unprecedented detail on Bing's China filtering practices.

The main findings from Xia’s research include:

  • Bing has a list of “forbidden” terms where no results are shown. 139 such terms have been identified.

  • Bing has a blacklist of websites that it never shows to China users. 329 such websites are identified. (5 have been lifted after our communication with Microsoft.)

Thu, Feb 13, 2014

Setting Bing's Broken Record Straight

We can also now trace complicit Bing Chinese censorship back to 2009 as highlighted by Nicholas Kristof. It looks like Microsoft has indeed changed its censorship mechanism after our research made headlines this week. But Bing is still seriously flawed on two fronts: its algorithm favors pro-Chinese government websites by default on all search terms in simplified Chinese and their front end mistakenly delivers explicit censorship of search results on some search terms for users from all over the world.

Wed, Feb 12, 2014

No error here: Microsoft deploying Chinese censorship on global scale

Microsoft says: “The results themselves are and were unaltered outside of China”. This is simply not true.

Tue, Feb 11, 2014

Bing practicing Chinese censorship globally

Our latest research indicates that Microsoft’s search engine Bing is censoring English and Chinese language search on its home page in order to exclude certain results. We have also noticed that Bing is practicing subtle censorship with search results. In both instances, Bing is filtering out links and stories that the Chinese authorities would deem damaging.

Thu, Jan 23, 2014

Massive blocking of foreign media in China

After Tuesday’s report Leaked Records Reveal Offshore Holdings of China’s Elite by ICIJ, China blocked a number of major newspaper websites. All websites below were blocked after publishing copies of the original report. They're all listed as the publishing partners for “Chinaleaks” stories on ICIJ's website. The Great Firewall rarely blocks non-Chinese websites. Many of them have published the Chinese version of the report which probably explains the unusual development.


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