u.s. intelligence law enforcement officials warn hackers tie russia intelligence service could try undermine credibility presidential election post document online purport show evidence voter fraud officials speak condition anonymity say however u.s. election system large diffuse antiquate hackers would able change outcome nov. election hackers could post document might falsify design create public perceptions widespread voter fraud officials say say specific evidence plan state local election authorities warn vigilant hack attempt oct. u.s. government formally accuse russia first time campaign cyber attack democratic party organizations interfere election process u.s. officials familiar hack direct american vote systems say evidence indicate suspect russian government-backed hackers far try attack voter registration databases operate 20 state trace attack difficult breach two databases confirm say officials say evidence hackers succeed access equipment databases use record vote many state use systems would difficult hack defraud include paper ballot initially tally machine u.s. elections run state local officials federal government nov. vote cast hundreds thousands poll station 9,000 different jurisdictions accord national association secretaries state u.s. officials decline comment republican candidate donald trump contention election rig trump say third final presidential debate democratic candidate hillary clinton wednesday night would say election result know whether would accept outcome trump campaign officials repeatedly say potential voter fraud remain high provide evidence thursday trump say would accept result election win say reserve right contest file legal challenge case questionable result clinton supporters say trump unwittingly aid effort russian president vladimir putin undercut credibility vote washington moscow odds several issue russian involvement ukraine conflict war syria cyber attack trump even know manipulate say michael morell former deputy cia director endorse clinton trump unwitting agent putin u.s. vote authorities warn alert russian hack fake fraud officials