The messages appeared on Facebook at the end of February, each making the same explosive claim: Taiwan’s government had lied about the number of coronavirus infections and deaths.

The posts, written in Mandarin, claimed an unnamed Taiwanese legislator was secretly revealing the cover-up. “I’m really angry right now, don’t the Taiwanese deserve to know these things?” the posts said.

The content from the Facebook posts were also shared on Weibo, a major Chinese social media platform, and similar claims spread on Twitter and YouTube.

The claim was false, and rapidly shown to be so by the Taiwan FactCheck Center, a nonprofit reporting organization. Taiwan’s government has not been lying about the number of cases, which currently stands at 44, including one death.

This claim, and other false ones targeting Taiwan, was part of a coordinated disinformation campaign launched by people in mainland China across multiple social platforms, according to researchers at the Digital Intelligence Lab at the Institute for the Future, a social science research group based in California. It offers new examples of Chinese internet users spreading fear and distrust in Taiwan over the deadly virus.

“Often the term [foreign interference] implicitly assumes a state actor, but this campaign appears to be a notable instance of a citizen-led, grassroots foreign disinformation attack,” said Nick Monaco, the head of the of Digital Intelligence Lab and a researcher of Chinese-language disinformation.

“Even in five years of looking at troubling disinfo every day, I'm not sure I've ever seen anything quite this malicious.”

As of now, there is no evidence of Chinese state involvement. Instead, it appears mainland Chinese internet users chose to target Taiwan with disinformation for patriotic reasons and online bragging rights. On its website, Taiwan’s Ministry of Justice said the campaign may have been inspired by a recent decision to curtail exports of face masks, which angered some in China.

Monaco said the campaign bore hallmarks of a Chinese troll group known as Diba.

“They organize ‘expeditions’ on forums and message boards,” Monaco said. “These expeditions involve large numbers of users jumping the Great Firewall to promote coordinated messaging, frequently targeting Taiwan and Hong Kong with patriotic — and often derogatory — Chinese messages, which often align with the official CCP party line.”

Diba’s Weibo account shared some of the false Facebook messages, but Monaco said he could not fully confirm whether the group created them.