In March 2009 former MSS operative Li Fengzhi told the Washington Times in an interview that the MSS was engaged in counterintelligence, the collection of secrets and technology from other countries, and repressing internal dissent within China. The internal repression, according to Li, includes efforts against nonofficial Christian churches and the outlawed Falun Gong religious group, plus censoring the Internet to prevent China's population from knowing what is going on outside the country. Li emphasized that MSS's most important mission is, "to control the Chinese people to maintain the rule of the Communist Party".
Chinese intelligence agents, probably under the control of the MSS, have achieved success in penetrating the U.S. Intelligence Community in the past. In the 1980s, Larry Wu-Tai Chin (Jin Wudai), a translator for the Foreign Broadcast Information Service of the CIA, was arrested and charged with espionage in the service of the PRC. He had been recruited in 1944 while stationed in China as a U.S. Army officer and went undetected for four decades. More recently, in 2003, Chinese-American Federal Bureau of Investigation source and Republican Party fundraiser Katrina Leung was arrested and accused of being a double agent for both the FBI and the Chinese government, although she was acquitted of charges of copying classified information, and convicted only of tax charges and of lying to the FBI.
In 2012, an executive assistant to MSS vice minister Lu Zhongwei was found to have been passing information to the CIA. Lu Zhongwei was not formally charged, but that incident was said to have infuriated Hu Jintao and led to a tightening on information dissemination and increased counterintelligence activities in Beijing and abroad.
The Shanghai State Security Bureau (SSSB) of the MSS has repeatedly been involved in both failed and successful attempts to recruit foreign agents. In 2010, the SSSB directed US citizen Glenn Duffie Shriver to apply for a position at the National Clandestine Service of the CIA. In 2017, SSSB case workers were implicated in the recruitment of US Department of State employee Candace Claiborne who was charged with obstruction of justice.
In 2017, the cyberespionage threat group known as Gothic Panda or APT3 was determined to have nation-state level capabilities and to be functioning on behalf of the MSS by researchers.
Economic espionage has become a prime directive of the MSS and the FBI has estimated that 3,000 companies in the United States are covers for MSS activity.[13] Companies such as Huawei, China Mobile, and China Unicom have been implicated in MSS intelligence collection activities.
In 2017, Ministry of State Security officials entered the United States on transit visas that did not allow them to conduct official business. During the visit the officials made an attempt to persuade Chinese dissident Guo Wengui to return to China. Guo Wengui accepted the meeting, out of apparent gratitude for one of the officials, named Liu Yanping, having previously assisted in bringing the wife of Guo Wengui to America. However, Guo Wengui recorded the conversations and alerted the FBI. Subsequently, the Chinese officials were confronted by FBI agents in Pennsylvania Station, the Chinese officials initially claimed to be cultural affairs diplomats but ultimately admitted to being security officials. The Chinese officials were given a warning for their activities in New York and were ordered to return to China. Two days later, the officials again visited the apartment of Guo Wengui once more prior to leaving the country. While at the apartment the second time, the officials reportedly ate dumplings made by the wife of Guo Wengui, and Guo Wengui walked them out of the building after again declining their offer of clemency for silence. The FBI was aware of the second visit and agents were prepared to arrest the Chinese security officials at JFK Airport prior to their Air China flight on charges of visa fraud and extortion, but arrests were not made following pressure from the State Department to avoid a diplomatic crisis. The FBI did, however, confiscate the Chinese officials’ phones before the plane took off.
https://en.wikipedia.org/wiki/Ministry_of_State_Security_(China)