The FBI squarely blamed Russian intelligence services Thursday for meddling in the 2016 U.S. presidential election, releasing the most definitive report yet on the issue, including samples of malicious computer code said to have been used in a broad hacking campaign.
Starting in mid-2015, Russia's foreign intelligence agency, the FSB, emailed a malicious link to more than 1,000 recipients, including U.S. government targets, the Federal Bureau of Investigation said in a 13-page report co-authored with the Department of Homeland Security.
While DHS and the Office of the Director of National Intelligence had said in October that Russia was behind the hacking, the report is the first detailed technical analysis provided by the government and the first official FBI statement.
The findings came the same day that President Barack Obama announced a series of retaliatory measures, including the expulsion of 35 Russian intelligence operatives and the sanctioning of the FSB and another Russian agency, the military's GRU.
The Kremlin denounced the sanctions as unlawful and promised "adequate" retaliation.
Among the groups compromised by the FSB hacks was the Democratic National Committee, which was again infiltrated in early 2016 by the GRU.
The report largely corroborates earlier findings from private cyber firms, such as CrowdStrike, which probed the hacks at the DNC and elsewhere, and is a preview of a more detailed assessment from the U.S. intelligence community that Obama ordered completed before he leaves office next month, a source familiar with the matter said.
Much of the information provided in the report is not new, the source said, reflecting the difficulty of publicly attributing cyberattacks without revealing classified sources and methods used by the government.
Some senior Republican leaders in Congress have expressed outrage at Russian interference in America's elections, diverging from their party's president-elect.
Throughout the raucous campaign, a steady stream of leaked Democratic emails clouded the candidacy of party nominee Hillary Clinton. In the aftermath of her defeat, Democrats have accused Russia. Meantime, Trump has questioned whether Russia was truly at fault.
The FBI said hackers gained access to and stole sensitive information, including internal emails "likely leading to the exfiltration of information from multiple senior party members" and public leaks of that information.
The report did not name hacked organizations or address previous conclusions reached by the Central Intelligence Agency and FBI, according to U.S. officials, that Russia sought to intervene in the election to help Trump defeat Clinton.
Trump has praised Russian President Vladimir Putin and has tapped people seen as friendly to Moscow for administration posts.
Russia has consistently denied the allegations of hacking.
"I would never expect Russia to come out with their hands up and acknowledge what they did," a senior administration official told reporters on a conference call. "They don't do that."