China is behind the largest known covert propaganda operation ever identified on Facebook and Instagram, according to a new report by security researchers at Meta.

Meta on Tuesday outed the authors of a four-year long influence campaign dubbed “Spamouflage Dragon,” which first appeared in 2019 to spread propaganda about Hong Kong’s pro-democracy protests. Since then, the campaign has focused on spreading disinformation about the origins of the COVID-19 pandemic, attacking dissidents and critics abroad, criticizing the United States, and attempting to sow division during the 2022 midterm elections.

For years, researchers have speculated that the voluminous Spamouflage Dragon posts were connected to the Chinese government but have been unable to publicly prove a link until now. The link comes courtesy of overlapping content found in both Meta’s report and charges filed against Chinese intelligence operatives back in spring.