The Times reported last January that Burisma had been hacked by the same Russian GRU unit that was one of two groups that hacked the Democratic National Committee in 2016. Last month, United States intelligence analysts contacted several people with knowledge of the Burisma hack for further information after they had picked up chatter that stolen Burisma emails would be leaked in the form of an “October surprise.”

Among their chief concerns, according to people familiar with the discussions, was that the Burisma material would be leaked alongside forged materials in an attempt to hurt Mr. Biden’s candidacy — as Russian hackers did when they dumped real emails alongside forgeries ahead of the 2017 French elections — a slight twist on Russia’s 2016 playbook when they siphoned leaked D.N.C. emails through fake personas on Twitter and WikiLeaks.

Facebook said that soon after the story was posted it noticed the controversy around the veracity of its claims and over how The Post had obtained the evidence. As the story circulated, the company said it had moved to tamp down its potential for virality.