Alleged hackers linked to Russia have been jointly sanctioned by the UK and EU.
Some 24 individuals and entities believed to be behind "destructive operations" have been targeted by the Foreign Office.
The EU said it was imposing restrictive measures on nine individuals and four entities, including officers of the Russian military intelligence service GRU, self-proclaimed "hacktivists" and cybercriminals.
Both EU member states and the EU have attributed a cyberattack on Poland's energy grid in the depths of winter to Russia's cyber-intelligence unit FSB Centre 16, the Foreign Office said.
Among the figures targeted by Britain are senior GRU officials Vyacheslav Stafeyev, Ivan Senin and Ivan Kasyanenko, who the Foreign Office said had directed the agency's cyber and hybrid threat operations.
It comes as the National Cyber Security Centre (NCSC) published a new advisory about the methods used by Centre 16 actors.
It said they had been "exploiting vulnerable routers and opportunistically targeting" networks belonging to critical national infrastructure.
The NCSC, part of GCHQ, said Centre 16 had also been seen "scanning the internet for devices that still use default or weak Simple Network Management Protocol (SNMP) passwords and community strings".
The NCSC urged the sectors most at risk of being targeted, such as communications, defence, energy, financial services, government and healthcare, to take action tighen up their defences by using the most secure version of the SNMP - SNMPv3 - and disabling legacy versions.
Read more from Sky News:
Jurassic Park star Sam Neill has died
Dozens killed in Bangkok bar fire - as likely cause identified
Foreign Secretary Yvette Cooper said: "These sanctions strike at the core of the cybercriminal networks propping up the Russian state's aggression, and the UK and EU are sending a clear message that Russia cannot hide behind its use of these proxy groups.
"From directing criminals to targeting businesses, and striking Poland's energy grid in the depths of winter, the Russian state is sinking to new lows in its attempts to undermine European security.
"Together with our partners, Britain will continue to call out this behaviour, bolster our resilience and respond to the hybrid threat posed by the Russian state. This will not deter us from supporting Ukraine."
(c) Sky News 2026: Alleged hackers linked to Russia facing UK and EU sanctions
World Cup: Ex-Spanish PM under fire for saying France has 'no French players'
Senators demand Pentagon reveals outcome of Minab school strike probe
Fifth British national identified as victim of wildfire in Spain
Wildfire of 'exceptional scale' breaks out in forest near Paris
'One of the greats': Jurassic Park star Sam Neill has died
Man wanted in UK over murder of wife and two children appears in South African court - as cause of death revealed
UK proscribes Iran's IRGC after 'threats to life' on British soil
Human trials of new Ebola vaccine set to begin in UK
Typhoon Bavi: Millions evacuated in China as severe flooding traps villagers and sweeps cars away
