lone hacker take responsibility cyber attack u.s. democratic national committee dnc cyber-security firm blame russian government dnc cyber firm crowdstrike disclose attack tuesday say hackers work russia break dnc computer network spy internal communications steal research presumptive republican presidential nominee donald trump russian government spokesman respond say moscow involve wednesday individual use moniker guccifer 2.0 take responsibility attack post blogging site wordpress.com say dnc hack lone hacker dnc respond request comment late wednesday even guccifer 2.0 claim crowdstrike say stand find russian government behind attack guccifer 2.0 blog include image document claim steal dnc servers include one title donald trump report date dec. 19 spreadsheets purportedly contain information party donors reuters unable verify authenticity document blog say among thousands file mail remove dnc servers would soon publish wikileaks crowdstrike issue statement say stand fully analysis two group affiliate russian intelligence discover dnc network last month company say review document publish guccifer 2.0 determine whether authentic 'lone hacker claim responsibility cyber attack democrats