An anonymous reader shares with us an exclusive report from Reuters: Yahoo Inc last year secretly built a custom software program to search all of its customers' incoming emails for specific information provided by U.S. intelligence officials, according to people familiar with the matter. The company complied with a classified U.S. government directive, scanning hundreds of millions of Yahoo Mail accounts at the behest of the National Security Agency or FBI, said two former employees and a third person apprised of the events. Some surveillance experts said this represents the first case to surface of a U.S. Internet company agreeing to a spy agency's demand by searching all arriving messages, as opposed to examining stored messages or scanning a small number of accounts in real time. 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. The two former employees say that the decision Yahoo CEO Marissa Mayer made to obey the directive resulted in the June 2015 departure of CISO Alex Stamos, who left to work for Facebook. The company said in response to Reuters questions about the demand, "Yahoo is a law abiding company, and complies with the laws of the United States."