It was an explosive conclusion which cast a pall over the entire election: that the Kremlin was behind a hack of the Democratic National Committee which resulted in its embarrassing secrets being published.
First made in June 2016, it has overshadowed the election, transition and now presidency of Donald Trump.
And the FBI, CIA, NSA and 12 other intelligence agencies published an unprecedented joint report saying the Vladimir Putin ordered a hacking campaign to tip the election against Hillary Clinton.
But now the first expert company to make a link between the DNC hacks and the Kremlin is facing a damaging series of questions over its credibility, DailyMail.com can disclose.
Cybersecurity firm CrowdStrike has had to retract portions of a report supporting its allegations of Russian cyberattacks – and is also refusing to address Congress about its findings on Moscow's election hacking.
Overshadowed: The entire election campaign from June onwards was hit by the Russian hacking and interference allegations, in a scandal which remains unresolved. But questions over the original source of a link to the Kremlin are revealed by DailyMail.com
Caught up: Debbie Wasserman Schultz called in CrowdStrike over fears the DNC was being hacked, which were confirmed. The firm then made the apparently definitive link to Vladimir Putin's Kremlin and remains the only one to have examined the DNC's servers
Resolute: The intelligence community under its Obama-era leaders of Director of National Intelligence James Clapper and CIA director John Brennan (right) concluded that Putin hacked the election to tip it in Trump's favor
Standing by his position: FBI Director James Comey told the House Intelligence Committee last month that the conclusion on Putin hacking the election was unchanged
CrowdStrike was hired by the Democratic National Committee to investigate suspicious network activity last May. In June it declared that the committee had been hacked by the Russian government, starting a firestorm over the campaign.
CrowdStrike, based in Irvine, California, is also the only group that the DNC allowed to directly examine its servers.
Not even the FBI has been granted access to the servers.
U.S. agencies have instead relied on CrowdStrike's work. There is no other known forensic evidence which has been publicly disclosed to link the Kremlin to the attacks, including in a series of intelligence community statements and reports.
But now questions are emerging about the reliability of the company's findings.
DailyMail.com can disclose that in March CrowdStrike quietly retracted portions of a December report that had made further Russian hacking claims, after the firm was found to have relied on inaccurate data posted online by a pro-Putin 'propaganda' blogger.
The errors prompted both the Ukrainian military and a prominent British think tank to issue public statements disputing CrowdStrike's data.
The errors, and retraction, surrounded a report in December which claimed that Fancy Bear, the same Russian hackers it said were behind the DNC attacks, were working on behalf of Russia's military intelligence agency, the GRU.
CrowdStrike said it found evidence that Fancy Bear had also hacked into Ukrainian military technology using the same software it used to infiltrate the DNC.
According to the report, the hackers were targeting an app used by Ukrainian soldiers to improve the efficiency of ther 122mm howitzers. The hack resulted in Ukraine losing 80 percent of these weapons in its ongoing low-level battle with Russian forces in the east of the country, the report said.
Alperovitch used an interview with the Washington Post to push the report and said: 'The fact that [these hackers] would be tracking and helping the Russian military kill Ukrainian army personnel in eastern Ukraine and also intervening in the U.S. election is quite chilling.
And Donna Brazile, the interim chairman of the DNC who had been revealed by the leaked emails to have given CNN's debate questions in advance to Hillary Clinton, and who then lied about it, highlighted the CrowdStrike report on Twitter, saying: 'Cybersecurity firm finds a link between DNC hack and Ukrainian artillery'