WASHINGTON — Further details of the extent to which Russian hackers targeted the 2016 U.S. election emerged this week.

Russian hackers gained access to electoral computer systems in 39 states, Bloomberg reported.

Illinois was among the first states to report the attacks. Officials there found evidence that hackers infiltrated the state’s voter database and tried to delete or alter data. Up to 90,000 voter records were compromised, according to Bloomberg.

The White House used the so-called “red phone” back channel to warn the Kremlin to stop the attacks. However, according to a leaked NSA document cited by Bloomberg, Russian hackers targeted the computers of 122 local election officials in the days before the Nov. 8 election.

The Obama administration believed the hackers may have been preparing to delete voter registration information to undermine confidence in the election, Bloomberg reported.

Earlier this week, former FBI director James Comey warned Congress that Russia would return to meddle in future U.S. elections.

Russia has denied any links to the cyberattacks.