The mercurial veteran GOP political operative, Roger Stone, has acknowledged that he is the unnamed Trump campaign regular who corresponded with an alleged Russian hacker, as described in a new indictment against a dozen Russians returned Friday by a federal grand jury.

The indictment by special counsel Robert Mueller targets 12 Russian intelligence officers for engaging in a sustained effort to hackDemocrats and aides to Hillary Clinton during the 2016 presidential campaign. All 12 defendants are members of Russia's intelligence service, according to the court filing.

The reference to a “U.S. person” who “was in regular contact with senior members of the presidential campaign of Donald J. Trump” describes emails exchanged with alleged conspirators, who were posing as the mysterious hacker Guccifer 2.0. In the brief exchange, the hacker told the Trump ally: “Thank u for writing back…do u find anyt[h]ing in the docs i posted?’”

“Please tell me if i can help u anyhow…it would be a great pleasure to me,’” the message said. “What do u think about the info on the turnout model for the democrats entire presidential campaign.’ The unnamed American responded, ‘pretty standard.’”

Stone said he believes the reference to that "U.S. person" in the indictment referred to him.

“As I testified before the House Intelligence Committee under oath, my 24 word exchange with someone on Twitter claiming to be Guccifer 2.0 is benign based on its content, context and timing,” Stone said when reached by ABC News late Friday. "This exchange is entirely public and provides no evidence of collaboration or collusion with Guccifer 2.0 or anyone else in the alleged hacking of the DNC emails, as well as taking place many weeks after the events described in today’s indictment,” he said.

The dates and content of the messages described in the indictment between the U.S. person in regular contact with senior members of Trump’s presidential campaign and Guccifer 2.0 match verbatim two screenshots Stone published on his website in March of 2017 of the direct message exchange he had with Guccifer 2.0 on Twitter in 2016.

At least seven people associated with longtime Trump friend Roger Stone have been contacted by Mueller, ABC News has determined through interviews with witnesses and others who confirmed they have been contacted.

Interest in Stone by federal investigators stems in part from his communications with Guccifer 2.0, a name used as a cover for a number of the Russians who are alleged to have hacked into DNC computers and then shared documents with the goal of hurting the Clinton campaign, sources told ABC News. Stone made statements in August of 2016 which political opponents have argued indicated he knew that Wikileaks was going to leak damaging information on Clinton before it was released.

The Mueller’s team appeared increasingly focused on whether any associates of Trump knew that the Russian government had hacked emails from the DNC and Clinton’s campaign chairman John Podesta and provided them to Wikileaks during the last presidential election, according to those sources.

In announcing the indictment Friday, Deputy Attorney General Rod Rosenstein said that although Americans corresponded with the indicted Russians, in this case, no Americans are accused of having knowingly conspired with Russian intelligence officers.

A self-described “dirty trickster” in American politics, Stone has taken credit for persuading President Trump to get into politics. He initially served as an adviser to Trump’s 2016 campaign but left amid controversy in 2015. While Trump told the Washington Post at the time that he “terminated Roger Stone...because he no longer serves a useful function for my campaign," Stone told a different story, explaining on Twitter their falling out was about political messaging.

Stone for his part has rejected any notion he was part of some grand conspiracy of collusion. When asked by ABC News in June whether he believed that Guccifer 2.0 was an operative of the Russian military intelligence, Stone denied it.

“I've written a 5,000 word piece you can see it stone cold truth that argues against that,” Stone told ABC News in an interview last month. “But even if he was, my communication with him is ex post facto it happens weeks after the WikiLeaks have already published the Democratic National Committee emails and therefore collusion would have to be, would have to be chronological.”

“Leaking after the fact,” Stone added, “impossible.”

“I think it is bad news for Roger Stone that his interaction with Guccifer 2.0 was recited in the indictment even though he was not named in the indictment,” Mitchell Epner, a former federal prosecutor who is now at the law firm Rottenberg Lipman Rich, told ABC News on Friday.

Just because Stone wasn’t named, does not mean it would signal one way or another if he is being looked at by investigators, Epner said.

“It is standard operating procedure that the DOJ does not name people in indictments unless they are being indicted,” he said.