A staff member removes the Iranian flag from the stage after a group picture during the Iran nuclear talks in Vienna, Austria July 2015. REUTERS/Carlos Barria Exclusive: 'Dumb mistake' exposed Iranian hand behind fake Proud Boys U.S. election emails - sources Media Industry Jack Stubbs WASHINGTON (Reuters) - Government analysts and private sector investigators were able to rapidly attribute to Iranian hackers a wave of thousands of threatening emails aimed at U.S. voters because of mistakes made in a video attached to some of the messages, according to four people familiar with the matter. Those failures provided a rare opportunity for the U.S. government to identify and publicly announce blame for a malicious cyber operation in a matter of days, something that usually requires months of technical analysis and supporting intelligence.