On Nov. 10, 2015, Preet Bharara, then the US attorney for the Southern District of New York, stepped behind a podium in the lobby of 1 Saint Andrew’s Plaza in Manhattan and made a stunning announcement. Flanked by agents from the FBI and the US Secret Service, he trumpeted the takedown of “one of the largest cyberhacking schemes ever uncovered.” JPMorgan Chase & Co., a pillar of the global financial system, had been hacked the year before by a gang that also infiltrated other marquee financial c...