Russian hackers feel the heat as Trump seeks warmer Moscow ties

Some U.S. officials, however, acknowledged that individual agents may now be more motivated to move against Russian cyber criminals following the election hacking scandal.

Russian hackers are active at all levels of cyber crime, from small-time thefts of online banking details, to taking down the computer networks of multi-national companies and government departments.

John Carlin, who until last October ran the national security division of the U.S. Justice Department as assistant attorney general, said resources had already been moving towards pursuing Russian nationals before the 2016 election.

But he added: "Their outrageous activity to undermine the integrity of our election, like they did in western Europe before and have done since, can only have added fuel to the fire."

According to interviews with five people who knew the men arrested this year -- all of whom declined to be named for fear of prosecution -- the arrests have shaken the Russian cyber crime community.

"Now they are arresting even those who had a super indirect, not even direct connection to what they call influencing their election," said one who knew Vinnik by his online moniker WME.

Used to operating across borders with relative impunity, Russian cyber criminals are now worried the prosecutions will lead to further arrests or harm their operations.

They are cutting back on trips abroad that were once seen as a calculated risk because of the risk of arrest and extradition, but are now viewed as increasingly foolhardy.

"We have monitored criminals discussing the aftermath (of the arrests) ... and it is clear they are concerned about two things," said Ilya Sachkov, head of cyber security firm Group-IB, whose Threat Intelligence unit specialises in monitoring and tracking the Russian-speaking cyber crime community.

"First, what the arrested members potentially know about them, but second and more importantly, a disruption in their ability to make money."

One of those arrested this year was Peter Levashov, charged by U.S. prosecutors with operating one of the world's largest botnets, or networks, of infected computers used by cyber criminals. He denies the charges.

Levashov allegedly used the botnet to pump out spam emails for a multitude of criminal schemes, such as stock fraud, online credential phishing attempts and the distribution of malware, including ransomware.

A person who knew Levashov by his online identity Severa said his arrest in particular had rattled underground cyber criminal circles because he was so well known.

"People read the news of course and see guys they know getting busted," the person said. "Once is bad, this many times is scary."