Ten minutes before the 2pm news broadcast on June 27, Vitaly Kovach, the editor of Ukraine's channel 24, stood up and told his staff to immediately unplug their network cables.

The computers had frozen at the channel's studio in Lviv, and an editor there had sent him a picture of what looked like a ransomware message.

But it was already too late to stop the virus from spreading: within minutes, 20 computers in the Kiev office were nonfunctional. The channel was under cyberattack.

“All the programmes froze, the video editing froze,” Mr Kovach recalled. “We were deaf, dumb and blind.”

Although international businesses were also compromised in the cyber attack, including the British advertising firm WPP, Ukraine was hit especially hard. More than 300 companies in the country would later say they were impacted.

According to Oleksii Yasinsky of the Kiev cybersecurity firm ISSP, Ukraine has become a “training ground” for suspected Russian hackers to “hone technologies, mastery and attack techniques” for bigger targets, including in the UK.

The head of the UK national cyber security centre said in November that Russian hackers had already tried to attack British energy, telecommunications and media companies over the past year.

Theresa May also reprimanded Russia over its cyber interference operations, a warning echoed by Boris Johnson during a visit to Moscow last week.