China has the world's most sophisticated censorship mechanism, and it can be very difficult for outsiders to understand how it works and what exactly is censored.
Several projects are devoted to shedding light on the situation by studying Sina Weibo, the most influential social media platform in China with more than 500 million registered users and 54 million daily active users, according to June 2013 figures. The China Digital Times has a “Ministry of Truth” section that collects directives from the country's propaganda authorities to media outlets and censored terms  in Sina Weibo's search engine.
WeiboScope through the Hong Kong University School of Journalism and Media Studies keeps track of the microblogs of 10,000 Weibo users with 10,000 or more followers and creates backups of those that are deleted . WeiboScope has opened their data for others to develop their own censorship monitoring projects, such as Free Weibo, which creates backups of censored microblogs and makes them available for search . Recently, Free Weibo developed a mobile app for mainland Chinese users to check out what has been censored.
The latest attempt to track Sina Weibo's censorship is ProPublica's Memory Hole  project. It uses software to monitor a set of 100 Weibo user accounts to detect censored images and visualize the censored content. As one might imagine, political speech is the largest category of censored images. The meaning of “political speech” covers everything from criticism of the Chinese government and calls for social justice to alternative interpretations of historical events.
In fact, other censored image categories that appear in the Memory Hole project, such as Dissidents  and Public Figures , Protests , Scandals & Corruption , Censorship  (meaning content that reveals what has been censored), and Cartoon & Humor , are all considered to be challenges to the legitimacy of the Chinese Communist Party, the major concern behind the party's recent call for online ideological battle.
All of the above research projects provide a brilliant overview of the country's censorship, but the data comes primarily from online opinion leaders — influential social media users who set the agenda and lead online conversation — and there is little information on how censorship affects grassroots initiatives. Community-based journalism on sensitive topics such as forced land acquisition, pollution, natural disasters, confrontations between street vendors and police, and small-scale protests against local authorities is also a vital part of the online conversation. Such content, often distributed by social media users who are not very active and have relatively few followers, might not catch the attention of opinion leaders on the national level, but the information has influence on the local level and is more directly connected with community-based social action.
Because the attention of Chinese web censors is focused more on national incidents that challenge the party's legitimacy, they tend to monitor celebrities who are capable of stoking public discussion nationwide, as well as hot topics that are already being discussed publicly throughout the country. Political deliberation in the national public sphere has been described as a process of “authoritative deliberation ” in which public opinion leaders act as the main channels of public opinion for the central government and so are able to pressure authorities for change.
However, apart from the national public sphere, social media has also enhanced the growth of regional-, community-, identity- and issue-based public spheres. A large number of non-verified microbloggers or those with fewer followers are active in publishing local news and witness accounts of incidents on Weibo, and they seem to run less of a risk of censorship until their posts go viral. Furthermore, some users, in order to spread their news, are engaged in a kind of online guerrilla warfare by making use of a number of non-verified accounts on different microblogging platforms. As most of the censorship monitoring projects are focused on the verified and influential users, how the censors deal with the more distributive grassroots sources is yet to be unveiled.
With the Chinese Communist Party refining its censorship strategy from filtering and deleting content post-publication to self-censorship by introducing new laws and regulations, such as the most recent rumor law, there has been a massive migration of netizens from Weibo to more private platforms such as WeChat. While WeChat also has a public platform, more critical conversations usually take place within closed private circles so as to prevent online smears and attacks.
Despite its appeal, many Chinese mobile users are aware of the fact that surveillance technology is embedded in WeChat, and that Chinese authorities could gain access to their chat logs , contact lists, messages, calls, and geographic locations. The application, with its horizontal privacy setting for group chat, does help users build communities according to different degrees of trust, and we are yet to find out how WeChat would change the online public sphere in China.