Russia and Iran are leading the way when it comes to pushing bad information on one of the world’s most popular social media platforms, and new analysis finds they are getting savvier at evading detection.

Facebook issued a report  looking at so-called coordinated inauthentic behavior over the past four years, warning that despite ongoing efforts to identify and remove disinformation networks, there is no let-up in attempts to exploit or weaponize conflict and crisis.

Overall, Russia was the biggest purveyor of disinformation, according to the analysis, with 27 identified influence operations during the four-year timeframe. Of those, 15 were connected to the St. Petersburg-based Internet Research Agency (IRA) or other entities linked to Yevgeny Prigozhin, a Russian oligarch with close ties to Russian President Vladimir Putin.

Another four Russian networks were traced to the Kremlin’s intelligence services and two more originated with Russian media sites.

Iran was second on the list, with 23 inauthentic networks, nine of which were connected to the government or Iranian state broadcasters.