Meta Platforms Inc. said it removed a China-based network of more than 500 Facebook accounts that sought to push a false narrative about the U.S. government’s attempts to blame the Covid-19 pandemic on China.

The campaign involved the fake persona of a Swiss biologist named Wilson Edwards, who in July posted on Facebook and Twitter Inc. that the U.S. was pressuring World Health Organization scientists to blame the virus on China, according to Meta’s monthly report on coordinated influence operations on its social networks.

Within days of the first post, hundreds of social media accounts and a handful of Chinese state media sources amplified the story about alleged American intimidation, Meta said on Wednesday. But the following month the Swiss Embassy in Beijing said there was no Swiss citizen by the name of Wilson Edwards, the company said. Facebook investigated and removed the account the same day.

Meta said it took down 524 Facebook accounts, 20 pages, four Groups and 86 Instagram accounts involved in the campaign, according to the report. The Menlo Park, California-based company said it found connections between the network and individuals in China, including employees of Sichuan Silence Information Technology Co. Chinese government officials also appeared to interact with the content posted by the network.

The social network also removed a group of accounts based in Italy and France linked with an anti-vaccination movement that targeted journalists, medical professionals and politicians.

Meta, formerly known as Facebook Inc., said bad actors continue to change their tactics to evade detection and enforcement action. One such strategy is known as “brigading,” where adversarial accounts work together to post or comment en masse in an attempt to harass or silence particular users. Another tactic these networks employ involves submitting a deluge of reports on an account or piece of content to get Meta to take it down.

“What we have seen consistently is that the threat actors behind these harms are evolving their techniques,” said Meta Head of Security Policy Nathaniel Gleicher. “We build our defense with this expectation in mind: they are not going to stop. They are going to shift their tactics.”