Here's what you need to know about the leak. How do we know this is the work of Russia? Cybersecurity experts who initially responded to the DNC hack identified two distinct groups of hackers operating in the system -- one who had exclusively gone after the party's opposition research file on Donald Trump, and one that had been snooping on DNC emails for about a year. Both were recognized as known Russian military or intelligence-affiliated hacking operations. Crowdstrike, the firm that responded to the hack, tracks dozens of advanced cyberespionage operations, many affiliated with governments. Each group has distinct ways...