https://techcrunch.com/2017/10/31/election-inference-shell-companies/

How can Internet giants know that innocent-seeming US companies aren’t actually shell vehicles for malicious foreign actors to buy ads to interfere with elections? The short answer is they can’t, and that drew questioning from a congressional probe today into Facebook, Twitter, and Google being used to manipulate the 2016 presidential election..

One member of the committee questioning the companies’ spokespeople asked: