In Some Countries, Facebook’s Fiddling Has Magnified Fake News

Last fall, the online giant altered what people in six nations see. Established news sites said their web traffic declined, adding that more bogus stories were shared instead.

SAN FRANCISCO — One morning in October, the editors of Página Siete, Bolivia’s third-largest news site, noticed that traffic to their outlet coming from Facebook was plummeting.The publication had recently been hit by cyberattacks, and editors feared it was being targeted by hackers loyal to the government of President Evo Morales.But it wasn’t the government’s fault. It was Facebook’s. The Silicon Valley company was testing a new version of its hugely popular News Feed, peeling off professio...