Washington: 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 US 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 on 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. Among them, Kozlovsky said he worked with the FSB to develop computer viruses that were first tested on large, unsuspecting Russian companies, such as the oil giant Rosneft, later turning them loose on multinational corporations.

Kozlovsky first came to public attention in early December when word spread about his confession in a Russian courtroom in August that he was the person who hacked into DNC computers on behalf of Russian intelligence.

He was jailed earlier this year, alleged to have been part of a hacking group there that stole more than $US50 million ($64 million) from Russian bank accounts through what's called the Lurk computer virus.