Congressional leaders were first made aware last year that Russian hackers had penetrated the Democratic Party officials' private information, but were unable to inform affected individuals because the intelligence was top secret, Reuters reported late Thursday.

U.S. intelligence officials forbade lawmakers from sharing their knowledge because they say it would have revealed to the Russians that American intel groups were monitoring the hackers and how they accessed private servers.

A group of eight lawmakers — four Republicans and four Democrats — were taken to a secure room called a Sensitive Compartmented Information Facility last summer, where they were informed of the breach. Among the Republicans were Senate Majority Leader Mitch McConnell, House Speaker Paul Ryan, and North Carolina Sen. Richard Burr and California Rep. Devin Nunes, who chair the House and Senate intelligence committees. The Democrats included Senate Minority Leader Harry Reid, House Minority Leader Nancy Pelosi, and California Sen. Dianne Feinstein and California Rep. Adam Schiff, both members of the intelligence committees.

Leaders of the Democratic National Committee were not even asked about the security measures around the group's server until last fall.

The public learned of the confirmed breach in June and WikiLeaks dispersed more than 20,000 hacked emails it received from an unnamed source in late July as Democrats prepared for their national convention in Philadelphia.

DNC Chairwoman Debbie Wasserman Schultz and other party leaders stepped down in the fallout from the leak, which indicated that party officials had favored and advocated for Hillary Clinton in the race over Bernie Sanders.