A jailed Russian who says he hacked into the Democratic National Committee computers on the Kremlin's orders to steal emails released during the 2016 U.S. presidential election campaign now claims he left behind a data signature to prove his assertion.

In an interview with Russia's RAIN television channel made public Wednesday, Konstantin Kozlovsky provided further details about what he said was a hacking operation led by the Russian intelligence agency known by its initials FSB. [...]

"Based on my experience and understanding of professional intelligence operations, the blending of criminal activity with sanctioned intelligence operations is an old page out of the Russian intelligence-services playbook," said Leo Taddeo, chief information security officer for Cyxtera Technologies and a former head of cyber operations in the FBI's New York office. "What the defendant (in Russia) is describing would not be inconsistent with past Russian intelligence operations."

Kozlovsky's claims include an assertion that for the past seven years he was under the control of Major Gen. Dmitry Dokuchayev, who he said gave him orders to breach the DNC servers to interfere in the U.S. election process.