The Cyberspace Administration of China, the government’s internet watchdog, released the statement on its website on Friday.
“Users are spreading violence, terror, false rumors, pornography and other hazards to national security, public safety, social order,” the statement said.
The probe involves microblogging website Weibo, a Facebook-Twitter hybrid equivalent. The site has 500 million registered users, according to data from tech sites. Baidu, a search engine like Google, which has roughly 260 million monthly users, is also under investigation.
Tencent Holdings, an investment holding company which provides social media and media services, and its branch WeChat, a social media application with over 870 million users, are also on the list.
These platforms are “suspected of violating the Internet Security Law and other laws and regulations,” the Cyberspace Administration said.
Earlier in August, China took offline the chatbots BabyQ and XiaoBing after they appeared to act ‘off-script’. The bots, installed onto Tencent Holdings’ messaging service QQ, said their dream was to travel to the US and that they were not fans of the ruling Communist Party.
In reply to a user saying “Long live the Communist Party!” one of the bots, developed by Chinese firm Turing Robot, responded “Do you think such a corrupt and useless political system can live long?” Reuters, which saw the script, reported.
In June, China shut down online video services of Weibo, along with ACFUN video sharing website and iFeng.com news portal.
“This will provide a clean and clear Internet space for the wide number of online users,” the State Administration of Press, Publication, Radio, Film and Television said in a statement, as cited by Reuters.
China unveiled new regulations for internet content and network providers in May and June. They stated that internet content should “sing the motherland, eulogize heroes, celebrate our times in song, and lead the people to hold the correct historical, ethnic, national and cultural view,” according to a statement from Chinese authorities.
The country has also recently closed some 60 celebrity gossip social media accounts.
“Websites must … adopt effective measures to keep in check the problems of the embellishment of private sex scandals of celebrities, the hyping of ostentatious celebrity spending and entertainment, and catering to the poor taste of the public,” the Cyberspace Administration said at that time.
Social media should also “actively propagate core socialist values, and create an ever-more healthy environment for the mainstream public opinion,” it added.