Tencent’s WeChat messaging app, which is extremely popular in its home market of China, censors messages that include certain key words related to some social issues and politics, even when users travel outside of the country.

According to Toronto-based Citizen Lab, messages pass through a remote server which contains rules for implementing censorship. If the message includes a keyword that has been targeted for blocking, the message will not be sent.

It found that while this only happens with accounts registered to mainland China phone numbers, such users “will remain under censorship regardless if they travel or unlink their Chinese phone number from the account”.

The organisation found that more keywords were blocked on group chats compared to one-to-one chat, “which suggests that communications on group chat are specifically targeted, potentially because group chats can reach a larger number of users”.

What’s more, users are no longer presented with a warning message when they enter blocked keywords, as indicated by previous reports.

“This change means there is no feedback to users that censorship has occured making the restrictions on WeChat less transparent,” the report observed.

Reuters contacted Tencent regarding the report but the firm simply said: “Tencent respects and complies to local laws and regulations in countries we operate in.”

China is of course known for its strict censorship rules, due to which Google, Twitter and Facebook services, amongst others, are banned.

Last week it was reported that Facebook quietly created a censorship tool that blocks posts from appearing in the news feed of users located in specific countries in order to make inroads into China.

Facebook has been blocked in China since 2009 and the country has since tightened its controls over the internet under President Xi Jingping.

Last month, Amnesty critised Tencent for being the only messaging app maker on its list that did not publicly state that it will not grant government requests to access encrypted messages by building a backdoor.

The Citizen Lab report also noticed that WeChat has made considerable efforts to grow its user base internationally but has yet to make the same impact in other countries as it has in its home market.

It said this may be because outside of China the app does not have “the same rich set of features, such as mobile payments and taxi hailing, that make it a compelling platform for users within China”.