Yahoo secretly monitored emails on behalf of the US government

Yahoo last year secretly built a custom software programme to search all of its customers’ incoming emails for specific information provided by US intelligence officials, sources have told Reuters.

The company complied with a classified US government directive, scanning hundreds of millions of Yahoo Mail accounts at the behest of the National Security Agency (NSA) or FBI, according to three former employees and a fourth person apprised of the events.

Some surveillance experts said this represents the first known case of a US 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.

Reuters was unable to determine what data Yahoo may have handed over, if any, and whether intelligence officials had approached other email providers besides Yahoo with this kind of request.

According to the two former employees, Yahoo CEO Marissa Mayer’s decision to obey the directive troubled some senior executives and led to the June 2015 departure of the chief information security officer, Alex Stamos, who now heads security 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.