Inside a US military cyber team’s defence of Ukraine

Russia failed to take down Ukrainian computer systems with a massive cyber-attack when it invaded this year, despite many analysts' predictions. The work of a little-known arm of the US military which hunts for adversaries online may be one reason. The BBC was given exclusive access to the cyber-operators involved in these global missions.

In early December last year, a small US military team led by a young major arrived in Ukraine on a reconnaissance trip ahead of a larger deployment. But the major quickly reported that she needed to stay.

"Within a week we had the whole team there ready to go hunting," one of the team recalls.

They had come to detect Russians online and their Ukrainian partners made it clear they needed to start work straight away.

"She looked at the situation and told me the team wouldn't leave," Maj Gen William J Hartman, who heads the US Cyber National Mission Force, told the BBC.

"We almost immediately got the feedback that 'it's different in Ukraine right now'. We didn't redeploy the team, we reinforced the team."