A senior US intelligence official told the BBC that there has been a sustained cyber-conflict over Ukraine that could still escalate.
Despite warnings, major cyber-attacks on the West have yet to occur.
However, Russia should not be underestimated, according to Rob Joyce, the National Security Agency’s director of cyber-security.
Meanwhile, he warned that independent hackers targeting Russia in support of Ukraine could spark an escalation.
“I’m still very worried about the threats emanating from around the Russia-Ukraine situation,” Mr Joyce, one of America’s most experienced cyber officials, said.
Initial surprise that Russia did not launch an all-out cyber-assault to cripple Ukrainian infrastructure as the war began has been replaced by an understanding that there has been far more aggressive activity than first thought.
“It wasn’t one massive attack. But there’s been a sustained conflict,” Mr Joyce explained.
Russia used eight or nine different viruses to wipe out computer systems. On Tuesday, the United States, the United Kingdom, the European Union, and other countries accused Russia of hacking a satellite communications provider used by the Ukrainian military, a hack that affected other customers in Europe.
However, Ukraine’s defences have held up relatively well, thanks in part to years of experience.
The cyber-clash, according to Paul Chichester, director of operations at the UK’s National Cyber Security Centre, is “the most sustained set of cyber operations coming up against the best collective defence we have seen.”
As many predicted, Russia has not responded to sanctions with cyber-attacks on Western companies or infrastructure.