https://www.reuters.com/article/us-usa-trump-russia-prevention/facebook-faces-big-challenge-to-prevent-future-u-s-election-meddling-idUSKCN1G102D

The Russian influence operation designed to tamper with the 2016 U.S. presidential election used a combination of old-school espionage tactics and 21st-century technologies that will not be easy to stop, even now that the methods have been exposed, experts said.