China has responded harshly to Deng Yuwen, a prominent Chinese exile writer living in suburban Philadelphia who has frequently criticized China and its authoritarian leader, Xi Jinping, with a crude and vicious online attack on him.

Through posts filled with sexual innuendo and threats, a covert propaganda network with ties to China’s security services has aggressively targeted not only Deng Yuwen but also his teenage daughter on the popular social media platform, according to researchers at Clemson University and Meta, the company that owns Facebook and Instagram.

The content was posted by users impersonating their identities and appeared in replies to Deng Yuwen’s posts on the social platform X, as well as in comments on the public school account in his community, in which Deng Yuwen’s 16-year-old daughter was falsely accused of being a drug addict, arsonist, and prostitute.

“It’s impossible to block it,” Deng Yuwen said in an interview, speaking in Mandarin about online attacks. “Because if you block it today, it will change its name and come back tomorrow.”

According to the researchers, vulgar comments about the girl also appeared on Facebook community pages and even on websites such as TripAdvisor, community news platform Patch and Niche, which helps parents choose schools.

The harassment fits a pattern of cyber intimidation that has alarmed Washington, Canada and other countries, where China’s attacks have become increasingly brazen. The campaigns include thousands of posts that researchers have linked to a network of social media accounts known as Spamouflage or Dragonbridge, organized by China’s vast propaganda apparatus.

“There’s no doubt that this crosses a line that they haven’t crossed before,” Linville said. “I think it shows that the line has become meaningless.”

“Even beyond China’s borders, including in the United States, they are exporting repression and human rights abuses — targeting, threatening and harassing those who dare to question their legitimacy or authority,” FBI Director Christopher Wray said at an American Bar Association conference in Washington in April.

He said China is exerting “incredible, almost mafia-style pressure” to try to silence dissidents currently living in the United States legally, including online and in-person actions such as posting leaflets near their homes.

Liu Pengyu, a spokesman for the Chinese Embassy in Washington, said in a statement that he was not aware of Deng Yuwen’s case and would not comment. He also said that the State Council issued regulations in China last year to protect the safety of young people online.

Meta said in a statement that it had removed the Facebook accounts targeting Deng Yuwen and his family as part of its monitoring of a “troll-like” campaign. The statement said the campaign had not attracted much attention on Facebook. Patch and Niche said they also removed the accounts for violating their standards of use. X and TripAdvisor did not respond to requests for comment.

Linville’s team at Clemson University said that not all posts targeting Deng Yuwen and his family have been deleted. New posts continue to appear, and even traces of deleted posts can remain online for years. For example, when searching for Deng Yuwen and his daughter on Google, the “water army disguised” attacks still appear.

Attacks from China have long been a challenge for U.S. government and law enforcement officials. Last year, the U.S. Justice Department indicted 34 officials working for China’s Ministry of State Security, accusing them of harassing U.S. residents like Deng Yuwen, but these officials live in China and may continue to work in China, outside the jurisdiction of U.S. law enforcement.

Some have called for a more aggressive response, including Michigan Rep. John Mueller, a Republican who chairs the House Select Committee on China.

“We need to educate and empower law enforcement and the American people to understand the Chinese Communist Party’s tactics,” he said in a statement. “And protect those who seek safe haven in our country.”

The “botnet” network was first discovered in 2019 during the massive anti-Beijing protests in Hong Kong. It creates fake accounts on social media or technology platforms and bombards real users with spam-like content – hence the name given to the network by researchers. While the content usually doesn’t go viral, the influx of attacks can be distressing or even worse for those targeted.

Last year, Meta linked the network to Chinese law enforcement, which once focused much of its attention domestically, discrediting and intimidating critics of the Communist Party, such as protesters in Hong Kong.

It has also become increasingly active overseas, trying to influence political debates and elections in Taiwan, Canada and, starting at least with the 2022 midterms, the United States. An American Olympic figure skater and her father, a former political refugee from China, have been the targets of what the Justice Department says is espionage ordered by Beijing.Chinese journalistespecially female journalists, have similarly appeared in false prostitution ads and faced bomb and rape threats.

The Justice Department indictment against the National Security Department officials did not explicitly link them to the troll network, but the activities are so closely tied to the troll work that it appears “highly likely” they are the same operation, according to a recent report by the Institute for Strategic Dialogue, a nonprofit research group. The institute also warned that the network is increasingly focused on the U.S. presidential election.

In the case of Deng Yuwen, as in others, the aim appears to be to stifle criticism. Mr. Deng, who was born in Xinyu in southeastern China, worked as an assistant editor at the Study Times, a weekly publication of the Central Party School that trains new officials.

His comments sometimes crossed the party line, and he was removed from office in 2013 after he wrote an opinion piece for the Financial Times calling on China to abandon its strategic relationship with Kim Jong-un, North Korea’s erratic authoritarian leader. He eventually left China.

Deng Yuwen, 56, has lived in the United States with his wife and two children since 2018. He continues to publish articles on Chinese politics and foreign policy in various news media and publish books on the subject. His latest book is The Last Totalitarian, published by New York’s Boden House in April. In the book, he argues that the Communist Party has lost the trust of the people and needs to reform.

Deng Yuwen said in an interview that he was used to criticism from Chinese officials, but the personal attacks began after he published an article in February in which he compared Xi’s team of senior officials to the “Gang of Four” under Mao Zedong.

The first post that Clemson researchers found appeared that month on X, where Deng’s account has more than 100,000 followers. It mentioned a middle school in his town and his daughter. The harassment spread to other accounts on X and then to many other platforms, including Facebook, Medium, Pinterest, DeviantArt and Pixiv, a Japanese artist website.

The posts denounced him as a traitor, a plagiarist and a tool of the United States. So far, more than 5,700 posts on X alone have mentioned his daughter, according to Clemson’s research.

These users often have profiles that make them appear to be American, but have few or no followers. Many of the posts are written in broken, ungrammatical English, a hallmark of a troll campaign.

They became increasingly lurid and threatening. Doctored images appeared on Facebook, superimposing Deng Yuwen’s daughter’s face on scantily clad women in sex ads that offered $300. At least one post called for her to be sexually assaulted and offered an $8,000 reward.

His daughter, a teen who speaks fluent English and is familiar with Gen Z slang, was initially outraged by the attacks, but with his encouragement, she, too, tried to ignore it. “I try not to involve my family in my affairs,” he said.

Meta, Google and other major technology platforms have long been aware of the activities of the “botnet” and have tried to weaken its influence. Last year, Meta announced that it had removed more than 7,700 fake accounts on Facebook associated with the network in just one quarter.

Clemson University’s Linville said China’s tactics are likely to continue because China “has not experienced any meaningful repercussions other than the account being shut down, which from their perspective costs them nothing at all.”