Fourteen former national security, intelligence and foreign policy officials filed an amicus brief in a lawsuit against the Trump campaign and GOP operative Roger Stone.

The brief, dated Dec. 8, was posted online Thursday by Business Insider and details how Russia uses "active measures" to spread disinformation and influence politics worldwide. It was filed by former senior officials, including former CIA Director John Brennan, Director of National Intelligence James Clapper, and National Security Agency Director Michael Hayden.

The brief was not filed on behalf of either party in the lawsuit, and officials behind the filing could not disclose classified information.

The lawsuit was brought against Stone and the Trump campaign in July by three private citizens whose personal information was hacked during a breach at the Democratic National Committee (DNC) last year and published on WikiLeaks.

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In the lawsuit, the plaintiffs allege that the campaign, Stone and "those they conspired with arranged for the hacked information to be provided to WikiLeaks."

Multiple congressional committees and a special counsel are investigating Russia's role in the 2016 election — in particular, whether the Trump campaign coordinated with Russian officials or representatives to sway the election in now-President Trump Donald John TrumpOmar fires back at Trump over rally remarks: 'This is my country' Pelosi: Trump hurrying to fill SCOTUS seat so he can repeal ObamaCare Trump mocks Biden appearance, mask use ahead of first debate MORE's favor.

The amicus brief filed this week discusses Russia's use of "cutouts" – intermediaries that facilitate active measure campaigns.

"These actors include political organizers and activists, academics, journalists, web operators, shell companies, nationalists and militant groups, and prominent pro-Russian businessmen," the brief reads.

"They range from the unwitting accomplice who is manipulated to act in what he believes is his best interest, to the ideological or economic ally who broadly shares Russian interests, to the knowing agent of influence who is recruited or coerced to directly advance Russian operations and objectives," it continues.

Those cutouts often facilitate the spread of disinformation and conspiracy theories in order to support the foreign policy and political interests of the Kremlin and sow distrust in democratic institutions, the brief reads.

Trump has denied any collusion between his campaign and Moscow, and has called special counsel Robert Mueller's investigation a "witch hunt." Stone, a longtime ally of Trump, has also denied improper dealings with Russia.

Mueller unsealed the first indictments in his Russia investigation last month, charging former Trump campaign chairman Paul Manafort and one of his associates with money laundering and tax evasion, among other things.

Michael Flynn, Trump's first national security adviser, also pleaded guilty this month to lying to the FBI about his contacts with Russia's ambassador to the U.S. in the month before Trump took office. George Papadopoulos, a former foreign policy adviser to Trump's campaign, also pleaded guilty to lying to FBI agents.