What form does Russian interference take? And how has a climate of “fake news” taken on a life of its own within the US?
Russian plans intended to help President Donald Trump could potentially exacerbate disputes around the results,especially if the race is too close to call.
With less than two weeks to the November poll,US officials say the two countries are trying to undermine the integrity of the election.
Facebook also warned that fraudsters from Albania to Vietnam are posting about US politics and the upcoming presidential election.
The New York Post published some of the emails,including one from an adviser to Ukrainian energy company Burisma,for which Hunter Biden once worked.
US intelligence agencies warned the White House last year that President Donald Trump's personal lawyer was a Russian intelligence target.
US prosecutors say the agency played a key role in Russian efforts to sway the 2016 election in favour of President Donald Trump.
Putin issued an unusual written statement outlining a four-point plan for a"reboot"in the field of information security,along the lines of a treaty.
Russia has repeatedly denied allegations of election meddling and says it does not interfere in the domestic politics of other countries.
Officials said the actions on Facebook so far were small and Beijing had not yet begun to mount a large operation on the US like Russia's this year.
Moscow views former vice-president Joe Biden as part of an anti-Russian American establishment.