A top secret National Security Agency document shows Russian military intelligence tried to hack into U.S. voter registration systems before last year's election, an online news service reports.
The Intercept reports that according to the NSA, the attempts went on for months and lasted until just days before the November 8 vote.
The targets were reported to be companies that provide voter registration services to local governments.
It is unclear how successful the hackers were. The NSA did not say whether their actions affected the outcome of the election — something U.S. intelligence says did not happen.
The Intercept did not say how it came to possess the leaked NSA report.
The Justice Department said Monday that federal authorities arrested a Georgia contractor named Reality Leigh Winner for allegedly "removing classified material" from a government "intelligence community agency" and mailing it to an "online news outlet."
Justice officials did not name the government facility or the news outlet.
The date on Winner's suspected mailing was five days after the date stamped on the NSA report.
U.S. intelligence already has determined that Russia hacked into Democratic Party emails and leaked embarrassing information to WikiLeaks in an apparent effort to help Republican Donald Trump win the presidential election over Democrat Hillary Clinton.
Congress and a special counsel are investigating whether anyone in the Trump campaign colluded with the Russians.
Russian President Vladimir Putin has denied the Kremlin meddled in the election.
However, he has conceded that Russian "patriots" with no ties to the government may have been involved in hacking.