SAN FRANCISCO — A top in-house lawyer at Facebook Inc. said Thursday the company is in a complicated game of cat and mouse with purveyors of “fake news” as it seeks to curb the spread of misinformation via its social media platform.

“Teasing out the false viral story from the true or accurate viral story is no small challenge,” said Facebook Deputy General Counsel Paul Grewal, speaking on a panel that closed out the Ninth Circuit Judicial Conference Thursday morning. “There is important economic and financial underpinning under this that are just as critical at getting to the bottom of as” the technological questions, Grewal said.