(Reuters) – Facebook Inc’s board backed Chief Operating Officer Sheryl Sandberg’s request to probe whether George Soros had shorted the company’s stock after the billionaire investor called the social network a “menace to society.”

“To be clear, Sandberg’s question was entirely appropriate given her role as COO,” Facebook’s board said in a letter on Wednesday. “When a well-known and outspoken investor attacks your company publicly, it is fair and appropriate to do this level of diligence.”

The letter was sent by Facebook’s general counsel Colin Stretch to Patrick Gaspard, president of Soros’s Open Society Foundations.

Sandberg was being truthful when she said she did not know that the social network hired a public-relations firm to explore Soros’s criticisms of the company, according to the letter.