Citizen Lab has analyzed how censorship works in the Chinese chat app WeChat:
- Keyword filtering on WeChat is only enabled for users with accounts registered to mainland China phone numbers, and persists even if these users later link the account to an International number.
- Keyword censorship is no longer transparent. In the past, users received notification when their message was blocked; now censorship of chat messages happens without any user notice.
- More keywords are blocked on group chat, where messages can reach a larger audience, than one-to-one chat.
- Keyword censorship is dynamic. Some keywords that triggered censorship in our original tests were later found to be permissible in later tests. Some newfound censored keywords appear to have been added in response to current news events.
- WeChat's internal browser blocks China-based accounts from accessing a range of websites including gambling, Falun Gong, and media that report critically on China. Websites that are blocked for China accounts were fully accessible for International accounts, but there is intermittent blocking of gambling and pornography websites on International accounts.
Lots more details in the paper.