ON SEPTEMBER 9TH a Chinese international student at Rice University in Houston found a nasty surprise waiting for her at her apartment. While she was out, someone had scrawled the word “spy” in capital letters across her front door, and again on the knocker.

She was “pretty scared,” says Iris Li, a childhood friend and fellow student in America who shared the pictures online. “She doesn’t feel safe in that community."

A day earlier America’s State Department had announced that it would revoke the visas of more than 1,000 Chinese citizens, in line with a presidential order issued in May.

This takes aim at students and researchers with links to any entity in China that “implements or supports” the country’s self-declared “military-civil fusion” strategy-a government effort to promote the flow of technology from civilian institutions for military purposes.

Chinese espionage is a real threat. In 2018 the Department of Justice stepped up investigations into Chinese spying, after it revealed that around 80% of all prosecutions for economic espionage were linked to China.

Since January the department has launched prosecutions in connection with at least 31 China-linked cases. The FBI opens a new China-related counterintelligence case every ten hours.

On September 21st it said a New York police officer, Baimadajie Angwang, had been charged with acting as an agent of China, spying on his fellow ethnic Tibetans.

The question is whether singling out students based on their educational background is an effective means of dealing with espionage. In 2018 President Donald Trump reportedly said that almost every Chinese student in America was a spy.

Most, but not all, of the people accused of espionage by the Department of Justice are Chinese nationals, although not necessarily students. Only eight students or researchers below professorial level have been publicly named this year.

Targeting students “is a blunt tool to deal with a very murky problem,” says Matt Sheehan of MacroPolo, part of the Paulson Institute, a think-tank in Chicago.

Those being stripped of their visas are a tiny fraction of the 370,000 Chinese students in America. Many are from universities connected to the People’s Liberation Army, including those affiliated with what the Chinese government calls the “seven sons of national defence”.

This is a group of universities overseen by the Ministry of Industry and Information Technology with “deep roots” in the armed forces and military-related industries, says Alex Joske of the Australian Strategic Policy Institute.

In China many schools and universities have military links, or at least historic ones. But the seven sons-among which are universities in Beijing, Harbin and Nanjing that specialise in military technology-are “almost hand in glove” with the Chinese government, says Mr Joske.

Nearly one-third of their 10,000 graduates each year join the defence sector. Many of the institutions have boasted about their achievements in military-civil fusion.

As a means of preventing espionage, the revocation of the students’ visas appears, to say the least, to have loopholes. A student already in America will not have to leave, but one who happens to be outside the country will not be allowed back in.

“The legal authority for visa revocation is discretionary,” notes Jeffrey Gorsky, a former chief legal adviser at the State Department’s visa office.

Many of the students complain that they have been unfairly treated, noting that they merely went to secondary schools with nominal military links before going to America for college.

Even those who had previously studied at national-defence universities in China should not be viewed with suspicion for that reason alone, says Yangyang Cheng, a particle physicist at Cornell University.

She studied at the University of Science and Technology of China in Hefei, a prestigious university involved in military-civil fusion, but not one of the seven sons.

They may simply have chosen those universities because they provide a good education, she says. One blogger in China joked that the list of universities treated by America as suspicious reads like a Who’s Who of China’s best academic institutions. “Many students are proud if their alma mater is on the list.”

The squeeze on students is a reflection of the Trump administration’s growing concern about what it sees as a security threat posed by Chinese citizens in America, particularly those working in fields that could be of interest to China’s armed forces.

On June 9th Tom Cotton, a Republican senator from Arkansas, introduced a bill that would ban Chinese nationals from postgraduate research in science, technology, engineering or maths.

“Chinese students and researchers contribute a huge amount to US research in computer science and engineering,” says Mr Sheehan. Were Mr Cotton’s proposal to pass, Mr Sheehan’s analysis predicts that the number of leading artificial-intelligence researchers in America would fall by one-third.

Perhaps the most prominent espionage case this year has involved not a student, but a professor, and an American one at that. Charles Lieber, the head of Harvard University’s chemistry department, was charged in July with lying about his involvement with China’s “Thousand Talents” programme, which aims to recruit scientists and engineers from abroad.

Mr Lieber was also accused of failing to disclose a monthly salary of $50,000 that he received from Wuhan University of Technology between 2011 and 2016. He has pleaded not guilty.

The Thousand Talents programme has been particularly controversial. America says it has facilitated the theft of intellectual property and the transfer of American technology to China.

The Centre for Strategic and International Studies, a think-tank in Washington, DC reckons the government may be “overstating the threat”, but calls the programme “opaque”.

In August 2018 the American government’s National Institutes of Health (NIH), an agency of the Department of Health, began investigating the foreign ties of NIH-funded scientists, including ones involved in the Thousand Talents programme.

By June this year they had raised concerns about 189 scientists, 175 of whom had failed to disclose support from China.

Taking aim at students won’t much hinder Beijing’s spooks. It is easy enough for spies to lie on visa application forms, and produce documents as evidence. But many Chinese students are anxious-all the more so amid rising xenophobia directed at Asians during the pandemic.

Ms Li, in her third year of philosophy at Emory University in Atlanta, is stoical. She plans to leave America after she finishes her degree. “I just hope I finish my studies soon, before everything turns into a dumpster fire.”