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We have been detecting which websites are blocked in China since February this year. Using our tool and contributions from our visitors, we've created the most complete database anywhere of what's blocked by the so-called Great Firewall of China, including 2200+ blocked websites and 200+ blocked searches. But how accurate is our data?

When a website is tested, it's always done by comparing the results of trying to access it from A) a computer outside China and B) a computer inside China. This way, a website that is simply not working is not labelled as blocked. A website that works when accessed outside of China but fails when tested from inside China, on the other hand, will be labelled as blocked.

This makes our data more accurate, but not perfect. Another difficulty is that the Great Firewall often changes temporarily. A given website that was previously accessible may be blocked for, say, 20 minutes. The opposite is also true. Blocked websites are sometimes temporarily accessible. Examples include Facebook (March 28, April 25) and YouTube (July 31, Aug 15 etc).

To tackle this particular challenge, our scripts always re-run testing of a website once more, after it's status has changed. In most cases, temporary changes are quickly detected and the websites are labelled correctly again. In some cases, however, if the change lasts somewhat longer, it may take up to a week for our system to re-label the website correctly. So, for example, Paypal was tested to be blocked twice on Aug 22. It's now accessible again. But it will take several days before our system automatically tests it again. Meanwhile, it's labelled as blocked.

In recent days news has spread that China is cracking down on VPN use (Guardian, Global Voices). Chinese internet users, particularly those in universities, are finding it increasingly difficult to make use of VPNs to circumvent online censorship and access blocked websites. This seems to be a continuation of the increased censorship witnessed this year, including temporary blocks of GMail and LinkedIn.

While important, this development leaves an obvious question unanswered: Why do the authorities not block access to the main websites of the major VPN providers? Each serious provider offers access to a number of servers around the world and blocking actual usage of these is somewhat complicated. The main websites, however, could be blocked in an instant. After all, the Great Firewall has no problem constantly blocking other websites such as Youtube and Facebook.

There are three apparent possibilites. The first is incompetence. The authorities might simply not be aware of the VPN providers that are not blocked. This seems unlikely for two reasons. First, all it takes is a Google search of, say, "VPN China". Blocking the top 10 results would go a long way to making VPN access in China more difficult. Second, some providers, such as StrongVPN, are in fact temporarily blocked from time to time.

At the time of writing, we're monitoring 59 Google searches that are all blocked in China. This means that when in China, unless you're on a VPN or proxy and you try to search for any of these words in Google, you'll be presented with a blank page. However, there's currently a glitch in the firewall which can be used to get complete uncensored Google search in China on a standard internet connection.

It's done using Google SSL. Google SSL is hosted on an encrypted server meaning that anything that is sent or received is out of reach of the Great Firewall. This is a good reason for the Chinese authorities to block the service altogether. They have of course, but there's a loophole. Here's how to do it:

1. Go to www.google.com/ncr

If you're in China, when you Google you're redirected to www.google.com.hk by default. Typing in www.google.com/ncr makes sure that you get to the international website and not the Hong Kong version.

2. Type in google encrypted and click "I'm Feeling Lucky"

This should take you to https://encrypted.google.com. Alternatively, you can try typing in that URL manually: https://encrypted.google.com.

A picture is worth a thousand words. The origin of this popular phrase may in fact be the Chinese proverb 一畫勝千言. So what would be a better way to communicate our analysis of the current online censorship in China than just that, in pictures? The wonderful online tool Wordle helped us do just that. If you click on any of the images you will see a larger version.

Websites blocked in China

First out is a visualization of major websites blocked in China. This was made using this list and by using the popularity of the website to give it more or less weight.

Searches blocked in China

Next up is a visualization of blocked searches. These are words and phrases deemed sensitive, meaning that if you search for any of them in Google while in China your connection will be reset and you'll only see a blank page. If you think the list is incomplete, please help us by adding a new search for testing.

All together

Our final visualization is a combination of major websites as well as searches blocked in China. If you have any ideas for other types of visualizations please feel free to comment.

The world-famous Chinese artist Ai Weiwei was arrested today. Here's a quick overview of what Chinese people can read about what happened, from behind the Great Firewall.

Basically, it comes down to language. English-speaking people can both search for his name and read the story on big news websites as well as check up on the background on Wikipedia.

In Chinese, it's much more sensitive. 艾未未, his name written in Chinese, is not (yet?) a blocked search, but researchers are prevented from accessing both his blog, the Wikipedia article in Chinese and news websites in the same language.

Increasing numbers of Chinese people use VPN's to get around the GFW. The majority of netizens in China who don't read in English and don't have a VPN are mostly limited to what the government wants to say about the story though. In this case, it seems to come down to complete silence.

The Great Firewall, referring to the online censorship managed by the Chinese government, is a sensitive topic. The authorities deny access to hundreds of websites and searches (and we do our best to keep track of which ones). But they also don't want their people to know that they do this. For this reason, they block access to websites that inform about how the censorship works. Two days ago, this websites joined the list of websites blocked in China.

However, we've set up a mirror website which, at this moment, is not blocked in China:

https://122.248.216.0

Because it's accessed through HTTPS, the GFW cannot automatically block access to it based on its contents. The so-called SSL certificate is invalid though, so you have to accept a warning message displayed by your browser to access it.

Our mirror website might also be blocked - time will tell (and our automatic monitoring, of course). But for the mean time, if you want to share any content on our website with VPN-less people in China, feel free to use the above link.

With over 600 million registered users, Skype is the worlds most popular online voice call service, and has also become the largest international voice carrier. Many people in China use it to keep in contact with friends abroad, as well as for international business calls. Importantly, voice calls as well as chats over Skype use a highly encrypted protocol which makes it difficult or impossible for the government to monitor what we say. In China though, as often is the case, there is a twist. Most Chinese users aren't in fact using Skype, but instead a client made by TOM, Skype's local partner.

What is TOM?

To the user, TOM looks very much the real Skype client. Behind the interface though, there are crucial differences. TOM is a company operating in China under Chinese regulations, meaning that all traffic is open to control by the government. Skype has been heavily critized for this cooperation, both in the media and on it's own forum. And here's a clip from NTDTV talking about the differences (in Chinese).

Dear reader. I know something about you. You are either not in the People's Republic of China - or you are using a VPN or proxy to bypass the Great Firewall. Otherwise, you wouldn't be reading this. Since yesterday, this website has been added to the list of websites blocked in China. As you can see to the right, other websites with information about the Great Firewall are blocked too.

Why, oh why?

Chinese people don't need this website to test whether a website is blocked or not - they can simply type in a URL or search and if it's blocked, the connection will be reset or timeout. Or do they? When a website doesn't work, it could be because it's blocked, but it could also be caused by the website itself. How can you tell the difference? You can connect your VPN and try again - or, you can test it on this website. A website is only marked as blocked by us if it 1) works when accessed from the US and 2) does not work when accessed from China.

Take, for example, the current difficulties of accessing Gmail in China. Our monitoring shows that this is caused by the Great Firewall - but the government has denied this and seem to want people to think that the problem lies with Google. Isaac Mao, a Chinese blogger, commented that the government is "testing the tolerance of the people" adding that "they cannot block Gmail totally, at this moment, because millions of people are using Gmail. If it is found that the government did this, people will react even more".

Indeed. So the government is doing what it can to prevent people from finding out.