Facebook said Tuesday it has identified a sprawling online propaganda effort: a pro-China campaign that had a presence on more than 50 websites.

The campaign “appears to be the largest known cross-platform covert influence operation in the world,” Meta said in a report. The researchers said the broadly coordinated postings of pro-China images, videos, comments and audio files were part of a yearslong operation that researchers had previously dubbed “Spamouflage.”

The findings underscore the potential for internet propaganda campaigns to attempt to exploit internet platforms to influence the U.S. election in 2024. Since 2016, Russia, Iran and to a lesser extent China have all launched covert online efforts to influence U.S. voters.