Yahoo last year secretly built a custom software program to search all of its customers' incoming emails for specific information provided by US intelligence officials, according to people familiar with the matter.
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 or FBI, two former employees and a third person apprised of the events said.
Some surveillance experts said this represented the first case to surface 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.http://www.businessinsider.com/r-exclusive-yahoo-secretly-scanned-customer-emails-for-us-intelligence-sources-2016-10