Podesta's Gmail account was hacked using a fake login page with a URL associated with the hacker persona Fancy Bear, which has been tied to Russian interests. The connection was first reported by Motherboard. Politico reported it had also confirmed with a cybersecurity firm the connection between Podesta's hacked account and Fancy Bear.
U.S. intelligence officials have said Fancy Bear was behind the months-long effort to hack the Democratic National Committee and other Democratic groups. Clinton charged in Wednesday's debate that Russia was hacking Democrats exclusively in a bid to help sway the election.
Fancy Bear was also behind the hack of former Secretary of State Colin Powell's email.
Podesta's email was hacked using what's known as a spear-phishing technique. Podesta was sent a fake bit.ly link that redirected him to a site built to look exactly like his usual Gmail login, but that instead enabled the hackers to get his password and recode his email to allow them access.
The same bit.ly URL was used in all the hacking attempts of the the DNC, Powell and other Democrats.
The result has been a series of thousands of leaked emails that have proven problematic for the Clinton campaign. They include frank conversations between aides about Clinton's strengths and weaknesses as a candidate, their thoughts on other people in the political world and transcripts of her closely held speeches to private groups, including the investment bank Goldman Sachs.
The emails were subsequently published by WikiLeaks.
Clinton has repeatedly called the Podesta emails illegal and criticized her opponent, Donald Trump, for using them against her, saying he has accepted the help of foreign adversaries to try to win the election.
"The new public data confirming the Russians are behind the hack of John Podesta's email is a big deal," Clinton senior adviser Jake Sullivan said in a statement Thursday. "There is no longer any doubt that Putin is trying to help Donald Trump by weaponizing WikiLeaks. Despite all the evidence, including the conclusions of the US intelligence community, Donald Trump went on the debate stage and acted as Putin's puppet, defending Russia and refusing to admit and condemn the Kremlin's actions. This behavior has gone from bizarre to disqualifying."