In the summer of 2019, a new Facebook user named Carol Smith signed up for the platform, describing herself as a politically conservative mother from Wilmington, North Carolina. Smith’s account indicated an interest in politics, parenting, and Christianity, and followed a few of her favorite brands, including Fox News and then-President Donald Trump.

Though Smith had never expressed interest in conspiracy theories, in just two days Facebook was recommending she join groups dedicated to QAnon, a sprawling and baseless conspiracy theory and movement that claimed Trump was secretly saving the world from a cabal of pedophiles and Satanists.

Smith didn’t follow the recommended QAnon groups, but whatever algorithm Facebook was using to determine how she should engage with the platform pushed ahead just the same. Within one week, Smith’s feed was full of groups and pages that had violated Facebook’s own rules, including those against hate speech and disinformation.

Smith wasn’t a real person. A researcher employed by Facebook invented the account, along with those of other fictitious “test users” in 2019 and 2020, as part of an experiment in studying the platform’s role in misinforming and polarizing users through its recommendations systems.