The Perfect Weapon: How Russian Cyberpower Invaded the U.S.

WASHINGTON — When Special Agent Adrian Hawkins of the Federal Bureau of Investigation called the Democratic National Committee in September 2015 to pass along some troubling news about its computer network, he was transferred, naturally, to the help desk.

His message was brief, if alarming. At least one computer system belonging to the D.N.C. had been compromised by hackers federal investigators had named “the Dukes,” a cyberespionage team linked to the Russian government.

The F.B.I. knew it well: The bureau had spent the last few years trying to kick the Dukes out of the unclassified email systems of the White House, the State Department and even the Joint Chiefs of Staff, one of the government’s best-protected networks.

Yared Tamene, the tech-support contractor at the D.N.C. who fielded the call, was no expert in cyberattacks. His first moves were to check Google for “the Dukes” and conduct a cursory search of the D.N.C. computer system logs to look for hints of such a cyberintrusion. By his own account, he did not look too hard even after Special Agent Hawkins called back repeatedly over the next several weeks — in part because he wasn’t certain the caller was a real F.B.I. agent and not an impostor.

“I had no way of differentiating the call I just received from a prank call,” Mr. Tamene wrote in an internal memo, obtained by The New York Times, that detailed his contact with the F.B.I.

It was the cryptic first sign of a cyberespionage and information-warfare campaign devised to disrupt the 2016 presidential election, the first such attempt by a foreign power in American history. What started as an information-gathering operation, intelligence officials believe, ultimately morphed into an effort to harm one candidate, Hillary Clinton, and tip the election to her opponent, Donald J. Trump.