On the bucolic campus of Purdue University in Indiana, deep in America’s heartland and 7,000 miles from his home in China, Zhihao Kong thought he could finally express himself.

In a rush of adrenaline last year, the graduate student posted an open letter on a dissident website praising the heroism of the students killed in the Tiananmen Square massacre in 1989.

The blowback, he said, was fast and frightening. His parents called from China, crying. Officers of the Ministry of State Security, the feared civilian spy agency, had warned them about his activism in the United States.

“They told us to make you stop or we are all in trouble,” his parents said.

Then other Chinese students at Purdue began hounding him, calling him a CIA agent and threatening to report him to the embassy and the MSS.

Kong, who goes by the nickname Moody, had already accepted an invitation from an international group of dissidents to speak at a coming online commemoration of the Tiananmen massacre anniversary. Uncertain if he should go through with it, he joined in rehearsals for the event on Zoom.

Within days, MSS officers were at his family’s door again. His parents implored him: No public speaking. No rallies.

Moody realized it didn’t matter where he was. The Chinese government was still watching, and it was still in charge. Just before the anniversary event, he reluctantly decided not to give his speech.

“I think that the Zoom rehearsals were known by the Chinese Communist Party,” he said. “I think some of the Chinese students in my school are CCP members. I can tell they are not simply students. They could be spies or informants.”

As the regime of Chinese President Xi Jinping reaches across borders to control its citizens wherever they are, its assaults on academic freedom have intensified, according to U.S. national security officials, academics, dissidents and other experts. Chinese intelligence officers are monitoring campuses across the United States with online surveillance and an array of informants motivated by money, ambition, fear or authentic patriotism. A comment in class about Taiwan or a speech at a rally about Tibet can result in retaliation against students and their relatives back home.

Students who don’t conform to the “views and ideology of the Chinese Communist Party,” said Mike Orlando, who leads the U.S. National Counterintelligence and Security Center, “risk being targeted for harassment.” China’s efforts to “suppress free speech and debate on U.S. campuses are concerning,” he said.

At Brandeis University near Boston, Chinese students mobilized last year to sabotage an online panel about atrocities against Uyghurs in the Xinjiang region. Viewers interrupted a Harvard-educated lawyer as she tried to describe her brother’s plight in a concentration camp, scrawling “bullshit” and “fake news” over his face on the screen and blaring China’s national anthem. To the dismay of participants, the university’s leaders failed to condemn the incident.

At the University of Georgia, a graduate student became the prey of an intelligence officer in China who pressured him over the phone to become a spy and inform on fellow dissidents in America. When the student made the conversations public, Chinese security forces harassed his family back home.

“It is real: the fear of being constantly watched, of being at risk,” said Chuangchuang Chen, a law student at St. John’s University in New York, whose dissident chat group on the encrypted Telegram platform was hacked. “If there are more than three or four Chinese students in the same class, you are scared to talk. A Chinese student is definitely seen in good favor by the Chinese government for reporting someone.”

U.S. law enforcement agencies have struggled to respond because much of the censorship and harassment occurs in a legal gray area. Victims are often frightened or don’t believe anyone can help. And university administrators are not always eager to intercede because it means risking a lucrative financial stream. U.S. universities have received more than $1 billion in donations from mainland China — from individuals, companies, government organizations — since 2013, according to the Department of Education. That doesn’t include tuition paid by Chinese students, whose numbers in the U.S. reached 370,000 in 2019. Moreover, the complexities of free speech and identity politics make administrators even more reluctant to confront Chinese state influence.

“It is easier to take a stance against the United States than against China,” said Rayhan Asat, the Uyghur scholar who was the target of the incident at Brandeis. “That is what is happening at U.S. universities. They are self-censoring themselves in order to recruit Chinese students for economic benefit.”

As a result, no one is doing much to prevent persecution by a foreign dictatorship in supposed bastions of learning and freedom, said U.S. national security officials, academics, dissidents and other experts.

“This is an overall extension of the police state,” said Anna Puglisi, a senior fellow at Georgetown University who served until last year as the U.S. intelligence community’s national counterintelligence officer for East Asia. “It is brazen. But when you talk about it, people act as if you’re nuts. There has been no cost to China for this.”

In 2019, university and national security officials met at a coastal resort in Maryland to discuss China-related threats. Many of the educators seemed oblivious to the repression in their midst, participants said. One skeptical administrator had never even heard of WeChat, the ubiquitous social media app used by Chinese students to communicate and by their government to shadow them, said Sophie Richardson, the China director of Human Rights Watch, who spoke at the conference.

“You realized how poorly understood some mainland students’ experiences are at U.S. universities,” Richardson said. “If the mainland students aren’t enjoying academic freedom to the same extent as others, that means universities are failing them. There is a certain amount of denial and a remarkable lack of awareness.”

Several university leaders who attended the conference declined to be interviewed. A rift between universities and the government over China worsened during President Donald Trump’s administration, whose policies were seen as hawkish and even racist by critics in academia. When then-Secretary of State Mike Pompeo gave a speech in December raising the specter of China meddling on U.S. college campuses — from stealing secrets to censoring students — some university officials dismissed it as overblown rhetoric.

“The reaction I was getting was: ‘This hostility with China, it’s Trump-driven. It will go away,’” said one U.S. intelligence official who talks with university leaders. “I said, ‘As long as Xi Jinping is in power, it will get worse.’”

Some educators, even China experts, warn against exaggerating the scope of the threat. Professor James Millward of Georgetown University, a historian of Xinjiang and critic of China’s repression there, witnessed the abuse of Asat at Brandeis. But he said he hasn’t seen that kind of aggressiveness in his own classes.

“I don’t have experience, in my teaching, of disruptions or hyper-nationalistic students,” Millward said. “My students and their parents are more concerned about anti-Asian hate, being attacked on the street. Most Chinese students just want to get educated and get on with their business.”

But recent studies by Human Rights Watch and the French Defense Ministry highlight increasing activity that exploits democratic freedoms across North America, Australia and Europe. Pro-China forces on campuses have assaulted, stalked, threatened and doxxed dissidents and scholars. Last month in Germany, a publishing company said pressure from Chinese diplomats caused two universities to cancel presentations of a biography of Xi written by German journalists.

The Chinese Embassy in Washington did not respond to ProPublica’s requests for comment. In the past, Chinese officials have denied allegations that they engage in censorship and spying at foreign universities.

To assess the extent of Chinese repression on U.S. campuses and the limits of the response, ProPublica interviewed Chinese students and scholars and reviewed emails, texts and other online communications that documented their experiences. ProPublica also spoke with current and former national security officials, educators, human rights advocates and other experts in the United States and overseas, and reviewed reports by governments, academics and human rights groups.

Most experts say U.S. and university officials could, and should, be doing more. Just as colleges shut down fraternities for hazing and other misconduct, they should crack down on wrongdoing by Chinese students associations, which often lead the attack on fellow students and proclaim their cooperation with the Chinese regime, the U.S. intelligence official said.

“I used to think universities were victims,” the intelligence official said. “But now I think those that take money from China and don’t protect their students from [People’s Republic of China] harassment may be complicit.”

Rayhan Asat was on edge.

It was Nov. 13, 2020. Asat, a lawyer specializing in human rights and international corruption cases, was looking forward to the panel sponsored by Brandeis University. She wanted to tell the story of her brother, Ekpar, a 35-year-old entrepreneur and one of more than a million people who have been imprisoned in the Xinjiang Uyghur Autonomous Region.

A roster of experts had assembled for the discussion on Zoom. Founded in 1948 by the American Jewish community, Brandeis seemed a receptive setting for a forum about the atrocities against the Uyghurs, an onslaught that the U.S. government has described as genocide.

But Asat was worried about rumblings of opposition. The Chinese students association had led the campaign, sending letters to the university president and others complaining about the event’s title, “Cultural Genocide,” and the “negative influence” on the Chinese community.

As the panel got underway, Asat recalled, she had a bad feeling. There were about 70 viewers. Many of them masked their identities with icons, including photos of Xi. During a talk by a professor from Indiana University, someone played a recording of the Chinese national anthem; the moderator kicked out the disrupter.

Finally, it was Asat’s turn. Launching into her PowerPoint presentation, she was ambushed. Insults appeared onscreen over the photos of her brother in a multicolored, crayonlike scrawl: “Bullshit,” “Fake News,” “hypocritical,” “rumors.” She felt as if an invisible hand were trying to erase Ekpar. The Chinese anthem blared again, another attempt to rattle her.

“It was incredibly disheartening,” Asat said. “I couldn’t control my screen. I kept talking. I was trying to maintain my composure, stay calm. I spoke for about 15 minutes, and it went on the whole time.”

The other panelists frantically communicated with one another and university technicians to try to stop the Zoom bombing by someone who was using the video conferencing program’s annotation feature.

“The only Uyghur on the entire panel was targeted,” said Leon Grinis, a student who organized the discussion. “They were definitely denying her voice and her story. I felt terrible for Rayhan. It was really admirable for her to push on and continue.”

The event, designed to highlight a horror unfolding in Xinjiang, ended up bringing attention to a harsh reality in the United States, Asat and other panelists said: widespread interference on U.S. campuses that is often directed or encouraged by the Chinese state.

Asat spoke at the invitation of Grinis, who was then a junior. Grinis said he is “partial to marginalized peoples” because his family suffered during the Holocaust in Germany and was persecuted in the Soviet Union. Using a $2,000 grant, he organized the panel of scholars, which included Millward, the Georgetown historian.

The repression of the Uyghurs, a predominantly Muslim group of Turkic ethnicity, has not spared elite families like Asat’s. She considers herself an advocate for her people but not an anti-China dissident. Her parents are loyal members of the Chinese Communist Party. Ekpar was a rising entrepreneur who developed a successful social media application in Xinjiang and took part in government-sponsored events there. In 2016, the State Department invited him to spend three weeks in the United States as part of its leadership program for talented foreigners.

After Ekpar’s return to China, however, the security forces abducted him, and he disappeared into the region’s vast complex of concentration camps. His family only found out last year that he had been sentenced to 15 years in prison on vague charges of “inciting ethnic hatred.” Asat believes authorities singled him out because of the State Department program. She has been working to free him since his imprisonment.

At Brandeis, students from China make up the largest group of foreign students, according to the university’s website. The campus has a robust Chinese Students and Scholars Association, which led the letter-writing campaign against the panel.

University computer technicians could not identify the culprits involved in the disruption because the panel had used Grinis’ personal Zoom account rather than a school account. But it became clear that the incident was not spontaneous. Apologetic Chinese students told Asat and other panelists privately that members of the CSSA mobilized to sabotage the event.

“They planned the whole thing,” Asat said. “They created a WeChat group for it. Everything was planned on WeChat.”

Asat suspects that students were not the only ones involved. “I can see the Chinese government’s hand behind it,” she said.

The Chinese government has played a role in similar incidents. In 2019, officials at China’s consulate in Toronto coordinated with the CSSA at McMaster University before a lecture by a Uyghur activist. On WeChat, the consular officials instructed students to identify Chinese nationals who attended, according to an investigation by The Washington Post. Students disrupted the speech and took photos and videos of the audience and provided them to Chinese officials. The university revoked the club status of the CSSA chapter as a result.

At Brandeis, hard evidence implicating the CSSA in the abusive behavior was lacking. But even after the ugly scene during Asat’s talk, Chinese students sent another round of letters to administrators criticizing the panel. A response sent by sponsors of the event, at the behest of Brandeis administrators, recounted what had happened. The strongest wording said that some audience members had asked questions in an “especially hostile manner that was offensive and disrespectful.”

Asat said she had expected the university’s top leaders to issue an emphatic public condemnation.

“I am disappointed that Brandeis didn’t find a way to make a very strong statement making sure this never happened again,” she said. “If this was an event about addressing racism or discrimination against any other marginalized or oppressed groups in America, I can imagine the reaction would have been different.”

Other participants agreed. Gordon Fellman, a sociology professor, said a response from the university’s president, Ronald Liebowitz, would have been appropriate.

“The university really didn’t condemn this,” Fellman said. “Many of us were puzzled. We thought it called for a strong condemnation.”

Because of the silence, Grinis contacted the student newspaper, which eventually wrote about the incident, as did Voice of America.

In an email, Brandeis’ assistant vice president for communications, Julie Jette, said the university had taken steps to prevent such a disruption from happening again.

“The interruption of last year’s panel including Rayhan Asat was entirely unacceptable,” she said. “Brandeis regrets that this occurred, and we strongly affirm our commitment to presenting multiple viewpoints and protecting free speech within our community.”

The university did not answer questions about why it did not respond more forcefully at the time of the incident or whether financial considerations related to Chinese students had an effect.

The Chinese Embassy and the Chinese students association did not respond to requests for comment.

Echoes of the incident still nag at Asat, who is now on a fellowship at Yale.

“Where do I seek justice?” she said. “Where do I go? I don’t have many platforms. My avenues of speaking are limited. One of them is universities.”

The diaspora of hundreds of thousands of students and scholars overseas poses a challenge for China.

On one hand, the communist regime wants and needs students at foreign universities to gather knowledge, especially in scientific and technical fields. On the other, it fears that they will absorb the influences of Western democratic ideas in the process.

To detect perceived anti-China activities, experts say, the authoritarian state has built a global machine that reacts in real time. The government’s well-documented ties to Chinese Students and Scholars Associations date from the 1970s, when the Communist Party created them “to monitor Chinese students and mobilize them against views that dissent,” according to a State Department fact sheet.

The associations are overseen by the “United Front Work Department, a sprawling worldwide network of party loyalists whose purpose is to influence local elites and community leaders,” according to the State Department. “Diplomatic posts often provide funding and guidance to individual CSSA chapters, such as directing members to disrupt lectures or events.”

In 2017, the CSSA at the University of California San Diego created an uproar about a commencement speech by the Dalai Lama, the spiritual leader of Tibet. The university stood firm, and the Dalai Lama spoke. In response, the Chinese government barred students and scholars on state-funded scholarships from attending the university, according to a report by the Hoover Institution at Stanford.

In June of this year, the CSSA at the University of Chicago complained that a speaking invitation to Nathan Law, a leader of the democracy movement in Hong Kong, showed “insensitivities and disrespect.” Law accused the group of being a tool of the Communist Party; the CSSA described itself as a “non-political, cultural organization.”

The associations do play a traditional role for many students on foreign turf, helping them find roommates, offering safety tips, recommending places to eat. At the same time, many chapters do not hide their official ties. From Cornell to the University of Michigan to Pasadena City College, CSSA social media pages make clear that the groups are “approved,” “recognized” and “supported” by the Chinese Embassy and consulates.

In a rare case in 2015, Columbia University disciplined its CSSA chapter, shutting it down briefly for unspecified “ongoing violations of multiple financial and student organizational policies.” The CSSA and the university quickly reached an agreement allowing the group to regain its official status.

Beijing has entrusted CSSAs with the vital mission of monitoring students and suppressing dissent — a system that functions with near impunity on U.S. campuses, according to national security officials, human rights experts, educators and dissidents. University officials tend to refrain from wading into the quagmire of conflict between dissidents and pro-regime students, who are in the majority.

“It is inconvenient for universities to recognize how pervasive this problem is,” said Puglisi, the former national counterintelligence officer for East Asia.

The FBI has jurisdiction over suspected foreign intelligence activity. But some acts — such as the persecution in China of relatives of a student in the U.S. — are not crimes here. If Chinese diplomats direct CSSA members to spy on their peers, prosecutors could theoretically file charges of acting as unregistered foreign agents, a frequent charge in espionage cases.

In practice, it’s unlikely, according to counterintelligence veterans. Diplomats have immunity. Surveillance of their interactions with informants on campus is difficult to use in the courts. Most resources go to battling China’s espionage offensive against government, scientific and corporate targets.

“What U.S. law is broken?” said retired FBI agent Joshua Skule, who led the agency’s intelligence directorate until two years ago. “Think how we would connect the dots. Parents say someone contacted them. How do we figure out who did something on U.S. soil? It’s hard. We are dealing with speech issues, academic environments that can be very touchy about law enforcement. Harassment might get reported, but it doesn’t rise in terms of FBI priorities on the China threat.”

The Chinese Embassy did not respond to ProPublica’s requests for comment. But when the U.S. government shut down China’s consulate in Houston for alleged misconduct last year, Chinese diplomats denied accusations by senior U.S. officials that consulates in the West supported counterdemonstrations related to Hong Kong, planted informants at universities and undermined free speech.

“The ‘China-supported counter protests,’ as claimed by the US, were spontaneous, rational patriotic actions by Chinese students in exercising their freedom of speech,” the Chinese Foreign Ministry said in a statement in July of 2020.

In fact, Chinese students don’t necessarily need orders from an intelligence handler to report on each other, experts said. They often do it spontaneously, their motives ranging from fear to ambition to sincere patriotism. Academic freedom protects pro-regime students as it does everyone else.

“There is self-censorship among my Chinese students,” said Elanah Uretsky, a professor of international and global studies at Brandeis. “There are things that they are willing to discuss with me in private but not in class. In classes on sensitive topics, I’ve also noticed that Chinese students are careful to be the only Chinese student enrolled in such classes. But I also have good conversations about Xinjiang in my classes that include a range of viewpoints among Chinese students.”

Even as a teenager in China, Zhihao Kong had doubts about the official version of history. He set up a virtual private network to access the internet, reading about the student protests in Tiananmen Square in 1989, when hundreds, perhaps thousands, of people died.

“I was very shocked,” he said. “Because I learned that the Tiananmen massacre had been totally different from what the Chinese Communist Party had taught us.”

While in college in China, he grew interested in Christianity and became a Protestant. His political awakening, meanwhile, began in earnest when he came to Purdue two years ago to continue his studies in engineering. Kong, whose nickname is Moody, said the trigger was the pandemic. Moody believed that China had worsened the outbreak by covering it up. The claims by Chinese leaders that COVID-19 had originated in the United States appalled him. In March 2020, he made a statement on social media: He condemned the regime for misleading the world and apologized in the name of the Chinese people.

“The most important thing is to stand up and speak out,” he said in an interview. “Not everyone has the opportunity to study here. I have the responsibility to say something. ... Those students who are in China, even if they are pro-democracy, they know that if they speak out, they will be detained immediately.”

That May, he went further. He posted his open letter invoking the heroism of the protesters killed by the People’s Liberation Army in Tiananmen Square 31 years earlier.

“The future of democratization in China remains bleak,” he wrote. “We are young Chinese students who share the values of democracy and freedom, and we are fortunate to learn the message of the free world thanks to God. Thirty-one years ago, students who fell at the gun of PLA on the streets of Beijing became a topic that China could not mention. ... We refuse to be silent.”

Days later, officers from the Ministry of State Security visited his parents.

His parents “were crying in the phone call. My father was urging me to stop such activities,” Moody said.

There were also repercussions on campus. Like millions of his peers, Moody spent hours on WeChat, the Chinese-language app that is its own world of social activity and information — and a target of surveillance. Moody had also posted his open letter on a chat group of the Purdue Chinese Students and Scholars Association, and the members went after him with a vengeance.

“Suspicion of participating in espionage organization that aims at overthrowing the government, we can call 12339,” wrote one student, according to a screenshot seen by ProPublica. The phone number is a hotline for reporting subversion to the MSS.

“For now you have violated PRC's ‘Anti-Secession Law,’” warned another student. “According to this law we can indeed report your real name.”

“Let’s vote to kick this person out,” chimed in a third.

Moody said he started avoiding other Chinese students. WeChat blocked or suspended his account several times.

Despite a growing sense of dread, he still wanted to play a role in the pro-democracy movement. His letter had caught the attention of a revered survivor of Tiananmen Square, who invited him to speak during an online commemoration of the anniversary of the June 4 massacre. Moody joined dissidents from around the world in rehearsals and planning sessions on Zoom.

Three days before the anniversary, his parents called again.

“My parents clearly told me do not accept interviews, do not attend activities,” he said. “I think the authorities knew my plans. I had to quit that meeting.”

His suspicions seem well-founded. In November 2020, U.S. prosecutors indicted a Chinese security executive who worked for Zoom in Zhejiang Province. They charged him with conspiring with MSS officers to identify U.S. planners of Tiananmen anniversary events by monitoring the rehearsals and gathering IP addresses. Intelligence officers then pressured dissidents not to speak at the events, harassing their families in China, court papers say.

Moody doesn’t know if he was a target in that case. But he thinks he was under surveillance at his school and by Chinese security forces monitoring communications.

Dissidents told ProPublica they agonize over the brutal choice of staying silent or speaking out. Chen, the St. John’s student, recounted a phone conversation with his mother after China’s secret police had harassed her about his activities in the U.S.

“My mother asked me: ‘What if I die because of this?’” Chen recalled. “I said, ‘If that happens, it’s not because of me, it is the Chinese government.’ When I decided to join a pro-democracy group here in 2012, I knew it would not be safe to go back to China. And I decided not to have much contact with my family, to protect them. I haven’t seen my family for nine years.”

Being new to activism, Moody said, he didn’t ask anyone for help. It might not have made a difference, based on the experience of a student at Florida State University.

In May, Yang Wang incurred the wrath of fellow students at FSU for posting a link on WeChat to a U.S. congressional hearing about atrocities against Uyghurs. Leaders of the CSSA insulted him, threatened to report him to the Chinese Embassy and news media, and kicked him out of their WeChat group, screenshots seen by ProPublica show. Twenty days later, he said, police visited his family in China.

Wang reported the CSSA to the university. An investigations office reviewed his complaint.

“They said they couldn’t do anything,” he said. “They said it was freedom of speech.”

Wang said he received no response to letters he sent to the FBI and a senator’s office.

Wang acknowledges that FSU officials reacted sympathetically, and he had a series of meetings and communications with them. They suggested that he could find kindred spirits at the campus branch of Amnesty International. One administrator said she had not met any other Chinese students who openly supported human rights causes, he recalled.

“She was surprised to see a student like me,” he said. “I think the university can’t do much. They want to help me. I can speak what I want to speak, but they can’t openly help me.”

ProPublica confirmed Wang’s account through records of his communications and interactions with university officials and students. FSU did not respond to questions from ProPublica.

In Indiana, meanwhile, Moody is coming to grips with his new reality.

“I knew I could get in trouble,” Moody said. “I didn’t know it could be so severe. My parents said they are probably banned from travel. And that I am banned from returning from China. They say I would be detained if I return. I am still young. I didn’t expect this to happen.”

Sulaiman Gu set a trap for a hunter.

It was January 2018. Gu, a graduate student in chemistry at the University of Georgia, had been preparing a bold scheme with a friend and fellow dissident living in Australia.

The friend had endured years of harassment by an officer of the Chinese Ministry of Public Security, which does domestic intelligence as well as police work, according to Gu and records he compiled. Based in Anhui Province, the officer had once arrested the friend during pro-democracy protests inspired by uprisings in the Arab world in 2011. Ever since, the officer had hounded him, continuing to call him and harass his parents in China even after the friend moved to Australia, Gu said.

The two young men decided that the friend would introduce Gu by phone to the police officer. They believed Gu was appealing bait because authorities knew him as an outspoken activist. They hoped to lure the officer into a conversation and try to confirm the existence of a rumored blacklist for students overseas.

“We pretended we were afraid,” Gu explained in an interview. “We said as dissidents we knew we were in trouble, and we wanted to come home to work.”

They attempted to find out if there was a blacklist by asking if they were on it, Gu said. Instead the spymaster “thought he could weaponize our fear.”

As Gu listened incredulously, the officer launched into a recruitment pitch on the phone. He warned Gu to stop talking about sensitive issues like Xinjiang and Tibet. But he said there was one shot at redemption: Gu could work as an informant. In phone conversations and text exchanges, the officer urged him to gather intelligence on pro-democracy activists in the United States. If he became a spy, life would improve for him and his relatives at home, said the officer, who identified himself as Xu Yongquan.

“In that way I can organize it and report it upward, so that those up there can know about your current thoughts and situation,” the officer wrote in a text seen by ProPublica. “This would change their opinion about you, it is beneficial to you coming back to China.”

Gu played along, recording and documenting the communications. He took the information to Radio Free Asia, which published a report. To Gu’s surprise, the officer called him afterward as if nothing had happened. Gu realized that he had not yet seen the story; apparently China’s censorship firewall limits the access of even the secret police to the Western press. The officer continued trying to recruit him for a few more days, sharing some personal details.

“He told me he was a learned guy,” Gu said. “He had graduated from law school. He was able to discuss ancient Roman laws, the British Parliament, ideas about different legal systems.”

Finally, the officer discovered that Gu had publicly outed him. In angry calls and texts, the officer called him “evil” and “a complete clown,” according to screenshots seen by ProPublica.

Soon, authorities in China retaliated, Gu said. They harassed Gu’s family and froze its control over a property in his name worth more than $300,000.

The Chinese Embassy did not respond to a request for comment about the case.

The episode fits an international pattern of Chinese security forces, often officers based in the provinces, attempting to recruit expatriates over the phone with threats as well as offers of money, leniency or bureaucratic favors, according to dissidents and national security officials.

But a scholar in the United Kingdom who has occasional contact with Chinese officials described experiences with different, more direct tactics. The scholar told ProPublica that intelligence officers ask about students — queries that the scholar politely evades.

“The activity is not even hidden anymore,” said the scholar, who asked to remain anonymous for safety reasons. “It is far more apparent and blatant. They want me to talk about my Chinese students. They are not even very shy about it. They want to know if they can sit in on classes to scope out the Chinese students. They ask: ‘Which Chinese students do you have, where are they from, what are you teaching them?’”

Unlike some dissidents who sound worn down by their struggle, Gu remains spirited and defiant. He calls out spies for stalking him and his fellow dissidents.

“Dear Chinese police,” he wrote in a tweet, “you won’t get my address as you repeatedly demand, but I’m glad to share that I live in a Castle Law state where a Chinese operative intruding a house can be legally shot by the resident.”

Gu has been politically engaged since his college years in China. He is a Hui Muslim from Sichuan Province. The Hui are a population of about 10 million who converted to Islam centuries ago and live in a number of provinces and regions, including Xinjiang. Traditionally, the Hui have suffered less oppression than the Uyghurs, but the government’s treatment of them has worsened in recent years.

For safety reasons, Gu declined to discuss whether he has had contact with U.S. government officials about his public clash with the Chinese police officer. But he said he feels safe in this country because the authorities are more vigilant here than in others.

“The repression is worse in Australia and Canada,” he said.

On some fronts, there has been progress in countering Chinese state interference at U.S. universities, experts say. Since 2014, American universities have shut down 89 Confucius Institutes, which are campus language and cultural centers controlled by the Chinese government, because of concerns that they engage in propaganda and censorship.

Universities and federal agencies have also improved cooperation against the theft of secrets by Chinese spies on campus, though some educators complain that U.S. law enforcement has overreacted.

But Richardson, the China director at Human Rights Watch, said that the priority for both academia and the government has been the espionage threat rather than “the more complicated conversation about censorship, self-censorship and academic freedom.”

Chinese students say they find themselves caught in the crossfire. Their police state stalks them; U.S. officialdom sees them as potential spies; anti-Asian hate crimes endanger them on the street. It can be a lonely and paranoid existence.

FBI agents try to be responsive, according to Chen and others who have dealt with them.

“The FBI is in contact with many dissidents here,” Chen said. “They try to get information. What they do is definitely not enough. I don’t blame the FBI. I believe the local police should get involved, they have more resources and local knowledge.”

Counterintelligence work is difficult, especially building prosecutions, but much of it takes place out of public view, officials said. Federal agents use a range of tactics to try to disrupt networks targeting students, such as blocking visas for suspects, intimidating them with visits or alerting universities to their operations.

“We have the authority to take more action on campuses, but it would be invasive,” the U.S. intelligence official said. “And the repression is a gray area in terms of legal and illegal. There is no one solution.”

One proposal popular among national security experts would encourage universities to give Chinese students U.S. cellphones upon arrival, protecting their privacy here and severing the electronic tether to China.

Meanwhile, some professors improvise protective strategies, such as allowing just one Chinese student per seminar group or publishing thesis papers anonymously. A graduate of one New York university recalled a professor warning her to wipe her essays about human rights from her computer hard drive if she returned to China.

Gu said there is a more fundamental problem at play: Pro-regime forces are skilled at exploiting the U.S. emphasis on political correctness, trying to persuade academic communities that criticism of authoritarianism in China equates to anti-Chinese bias.

“American universities tend to treat these issues as issues of racism and diversity,” Gu said. “The university should support students against the surveillance of a foreign government. They should take measures to let educated and legitimate opinions be expressed without fear.”

Kirsten Berg contributed research.