Facebook faces big challenge to prevent future U.S. election meddling

FILE PHOTO - A Facebook logo is seen at the Facebook Gather conference in Brussels, Belgium January 23, 2018. REUTERS/Yves Herman

SAN FRANCISCO/WASHINGTON (Reuters) - 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.

Social media companies, especially Facebook Inc and Twitter Inc , have been under heavy pressure to find ways of stopping what is often referred to as "information warfare" on their services.