Ahead of the annual Blueberry Festival in Marshall County, Indiana, in early September, a woman broadcast a warning to her neighbors on Facebook.
"I just heard there's supposed to be a mass shooting tonight at the fireworks," the woman, whose name is held to protect her privacy, said in a post in a private Facebook Group with over 5,000 members. "Probably just a rumour or kids trying to scare people, but everyone keep their eyes open," she said in the post, which was later deleted.
There was no shooting at the Blueberry Festival that night, and the local police said there was no threat. But the post sparked fear in the community, with some group members cancelling their plans to attend, and shows the power of rumours in Facebook Groups, which are often private or closed to outsiders. Groups allow community members to quickly spread information, and possibly misinformation, to users who trust the word of their neighbors.
These groups and other private features, rather than public feeds, are "the future" of social media, Facebook Inc Chief Executive Mark Zuckerberg said in April, revealing their importance to Facebook's business model.
The threat of misinformation spreading rapidly in Groups shows a potential vulnerability in a key part of the company's growth strategy. It could push Facebook to invest in expensive human content monitoring at the risk of limiting the ability to post in real time, a central benefit of Groups and Facebook in general that has attracted millions of users to the platform.
When asked if Facebook takes accountability for situations like the one in Indiana, a company spokeswoman said it is committed to maintaining groups as a safe place, and that it encourages people to contact law enforcement if they see a potential threat.
Facebook Groups can also serve as a tool for connecting social communities around the world, such as ethnic groups, university alumni and hobbyists.
Facebook's WhatsApp messaging platform faced similar but more serious problems in 2018 after false messages about child abductors led to mass beatings of more than a dozen people in India, some of whom have died. WhatsApp later limited message forwards and began labelling forwarded messages to quell the risk of fake news.