This post was written by Marcus Wang and Stella Fan of the WeChatscope, a research initiative at The University of Hong Kong. This article is the first in a partnership series  with Global Voices.
In China today, it is nearly impossible to live one's life without WeChat. What began as a chat app, similar to WhatsApp or Facebook Messenger, has become an essential tool for conducting many everyday activities, from communication to basic purchases and bill payment.
WeChat has the largest number of domestic users and the most extensive coverage of any social media service in the country. According to data released by WeChat , the company now boasts more than 1.0825 billion  individual users, along with more than 20 million  registered public accounts.
In addition to regular citizens who typically maintain personal WeChat accounts, nearly all government departments, state-owned organisations, private entities and local communities have registered “public” accounts on WeChat, where they produce content similar to Facebook pages. This creates an open space for quasi-public discussions about a wide range of topics such as personal stories, social issues, sports, technology and breaking news. Individual users closely interact with public accounts by leaving comments and forwarding the posts to social groups.
In 2018, an estimated 500,000 WeChat official accounts  were active every day, with roughly five billion daily page views. WeChat's mobile payment system has become China's preferred method for payments of all kinds, due to the app's convenience and the sharp rise in the circulation of counterfeit currency in the country.
WeChat's massive user base and powerful social influence have also helped it to become a chief component of China's rigorous censorship regime. In 2017, our team  at the University of Hong Kong built a technical web “scraping” system for studying censorship on WeChat's publicly accessible pages. Throughout 2018, we preserved censored posts in a publicly accessible database. We call it WeChatscope .
Our team tracked more than 4,000 public accounts covering daily news through our computer program which visits (and periodically revisits) published articles and records the contents. When the system sees that a post has disappeared, it is detected as censored. A copy of the post is then restored in the database and made available for public access.
By the end of 2018, a total of more than 1.04 million articles were included. Out of these, roughly 11,000 have been removed by the internet censorship system.
This approach allows us to detect content that was removed after it was posted — but it misses content that was censored prior to publication. The majority of Chinese social media platforms are equipped with a keyword filter that allows them to automatically censor sensitive information before it is published. A list of keywords is created and constantly updated by state censorship authorities, and then handed down to platform operators. This explains why certain politically sensitive topics such as the Xinjiang re-education camps rarely appear in our dataset.
While the volume of content blocked by keyword filtering is large, by analyzing the available content data, the project can still serve as a barometer China’s overall social media censorship regime.
Four official reasons for WeChat censorship
After a post is removed from WeChat, the company issues an official explanation of the removal to its authors and readers. The company typically offers one of four different reasons:
- “This content has been deleted by the publisher” (8,092 articles)
This message indicates that the author removed their own posts. Self-censorship is a common practice among internet users in China as online speech can easily bring them trouble. Posts that cite unofficial sources of information can easily be charged with spreading rumors if they are re-posted more than 500 times. Users will often remove their own posts if they receive warning from senior colleagues or employers.
- “This content is unavailable for violation of related law and regulations” (2,950 articles)
This message indicates that either the censorship authorities or the corporate content review team found and removed illegal contents.
- “This account was blocked” (406 articles)
If a user has violated community rules several times, the related account will be suspended or terminated. The censorship authorities could also request platform operators to block a user's account directly.
- “This content has been reported by multiple people, and the related content is unable to be shown” (206 articles)
Content can be removed if other users flag it for violating platform rules.
10 controversial topics in 2018
Upon examining our full 2018 data set, the research team found that the scope of topics censored on WeChat has expanded from domestic policies and social unrest to less politically sensitive topics, in what seems to be an effort to support China’s international political image as a “great power”. The most sensitive topics of 2018 included:
- China-US trade war
- US sanctions against ZTE
- The arrest of Meng Wanzhou, CFO of Huawei in Canada
- The investigation of businessman Ye Jianming for economic crimes
- Hongmao medicinal liquor scandal
- #Metoo and sexual harassment allegations against a Peking University professor
- Passenger-driver conflict in Chongqing
- World’s first genetically-edited baby
- Changsheng vaccine scandal
- Fan Bingbing tax fraud scandal
In this forthcoming series, we will highlight the top 10 censored topics in 2018, one article at a time.