The Chinese government is well known for keeping tight control over what both media and individuals can say publicly. Monitoring and censorship is widespread, but a recent study carried out by the Citizen Lab at the University or Toronto, reveals censorship is happening in real-time without any knowledge by Chinese users chatting to each other online.

The Citizen Lab's study focused on the WeChat instant messaging service. WeChat is classed as an instant messaging service, but it also offers voice messaging, video conferencing, the ability to share media files, and a built-in Web client for surfing the Internet. It is hugely popular, with over 800 million active users, the majority of which are located in China.


WeChat, as with every other online service in China, is censored and has been for years. Users are used to seeing warning messages informing them a message they tried to send was blocked due to restricted word use. However, that censorship is now happening without the warning, and therefore without user knowledge.

Censorship carried out on WeChat happens on the server side. So one user sends a chat message and sees it appear in the WeChat client as if it has been received. Meanwhile, the message passes through a server where it is checked for any restricted words. If any are found, the message is not sent on to the user and neither party is told.

The Citizen Lab needed to carry out a range of test scenarios in order to confirm this was happening as there's no way to access WeChat servers directly. The results show that WeChat accounts registered to mainland China phone numbers experienced the silent filtering of messages. International accounts could be censored, but nowhere near as much as mainland accounts. Group chats are also censored more heavily than one-on-one chats. This is believed to be because group chats allow for more influence due to a large number of people being involved in the discussion.

The filtering was also found to be dynamic. So on particular days or for set periods of time, new restricted words or phrases can be added or removed. This allows censorship to quickly adapt and easily deal with difficult breaking news, for example. As to how much content is blocked, the Citizen Lab found 174 keywords, a full list of which can be found on GitHub.

This latest study builds on previous work done by the Citizen Lab last year when it found WeChat censorship started heavily targeting politics and rumors discussions. Now it seems, anything and everything is being targeted, and nobody except the governments censors know when it happens.