https://www.cnbc.com/2017/10/13/new-york-times-digital-how-facebooks-ad-system-works.html

In early September, Facebook revealed that it had identified about $100,000 in ads purchased on its social network by a Russian company linked to the Kremlin. Distributed between June 2015 and May of this year, the more than 3,000 ads added to evidence that Russia interfered with the 2016 presidential election.

Similar ad purchases by Russian agents were also uncovered on other internet services like Google and Twitter.