https://arstechnica.com/tech-policy/2017/10/facebook-google-and-twitter-tell-congress-they-spread-russian-propaganda/

Top officials from Facebook, Google, and Twitter told a congressional panel Tuesday that their platforms hosted a disinformation campaign carried out over their networks by Russian state actors. The propaganda centered on the presidential election, immigration, gun rights, gay rights, and racial issues, the companies said. None of the three organizations said they supported proposed legislation requiring them to disclose who is buying political advertisements on their platforms, although these Web companies promised more public transparency about who is buying ads on their networks.