An investigation by the New York Times found that the phishing campaign was detected but a typo by party aide saw the malicious email labelled as ‘legitimate’ instead of ‘illegitimate’.
The mistake gave the hackers access to around 60,000 emails that were subsequently passed to the WikiLeaks and published in October.
The New York Times said: “An examination by The Times of the Russian operation – based on interviews with dozens of players targeted in the attack, intelligence officials who investigated it and Obama administration officials who deliberated over the best response – reveals a series of missed signals, slow responses and a continuing underestimation of the seriousness of the cyber attack.
The email hack became a big story during the US presidential election and was used by the Republican president-elect Donald Trump to attack his opponent.
“While there’s no way to be certain of the ultimate impact of the hack, this much is clear: A low-cost, high-impact weapon that Russia had test-fired in elections from Ukraine to Europe was trained on the United States, with devastating effectiveness.”