Britain has publicly blamed the Russian government for a cyber attack which targeted Ukraine and spread across Europe last year.
The NotPetya attack's primary targets were the Ukrainian financial, energy and government sectors but it was designed to spread further and affected other European and Russian firms in June 2017.
Ukraine has been locked in a simmering conflict with Russian-backed separatists since Moscow annexed Crimea in 2014.
Defence Secretary Gavin Williamson said: "We have entered a new era of warfare, witnessing a destructive and deadly mix of conventional military might and malicious cyber attacks.
"Russia is ripping up the rule book by undermining democracy, wrecking livelihoods by targeting critical infrastructure, and weaponising information.
"We must be primed and ready to tackle these stark and intensifying threats."
The foreign minister for cyber security, Lord Ahmad of Wimbledon, said the UK's decision to identify the Kremlin as responsible for the attack underlines the fact the Government will not tolerate "malicious cyber activity."
He said: "The UK Government judges that the Russian government, specifically the Russian military, was responsible for the destructive NotPetya cyber attack of June 2017.
"The attack showed a continued disregard for Ukrainian sovereignty. Its reckless release disrupted organisations across Europe costing hundreds of millions of pounds.
"The Kremlin has positioned Russia in direct opposition to the West yet it doesn't have to be that way.
"We call upon Russia to be the responsible member of the international community it claims to be rather then secretly trying to undermine it."