
It is not known what information intelligence officials were looking for, only that they wanted Yahoo to search for a set of characters. That could mean a phrase in an email or an attachment, said the sources, who did not want to be identified. Reuters was unable to determine what data Yahoo may have handed over, if any, and if intelligence officials had approached other email providers besides Yahoo with this kind of request.
According to two of the former employees, Yahoo's decision to obey the directive led to the June 2015 departure of Chief Information Security Officer Alex Stamos, who now holds the top security job at Facebook.
"Yahoo is a law abiding company, and complies with the laws of the United States," the company said in a brief statement in response to Reuters questions about the demand. Yahoo declined any further comment.