The UK government has accused Russia’s military intelligence service of being behind four high-profile cyber-attacks.
The National Cyber Security Centre says targets included firms in Russia and Ukraine; the US Democratic Party; and a small TV network in the UK.
A Russian foreign ministry spokeswoman described the accusation as a “rich fantasy of our colleagues from Britain”.
World Anti-Doping Agency computers are also said to have been attacked.
Files later emerged showing how British cyclists Sir Bradley Wiggins and Chris Froome had used banned substances for legitimate medical reasons.
At the time, some of the attacks were linked to Russia – but this is the first time the UK has singled out the GRU, the Russian military intelligence service.
British police think the men who carried out the Salisbury poisoning in March worked for the same group.
Speaking on behalf of the Russian foreign ministry, Maria Zakharova said the UK’s accusations were “mixed in one perfume bottle”, adding: “Maybe a Nina Ricci bottle: GRU, WADA, Kremlin hackers – it’s a diabolical perfume.”
But Defence Minister Gavin Williamson condemned Russia as a “pariah state”, and said Moscow’s “reckless and indiscriminate” attacks had left it isolated in the international community.
The NCSC said it has assessed “with high confidence” that the GRU was “almost certainly responsible” for the cyber-attacks.
Foreign Secretary Jeremy Hunt said the GRU had waged a campaign of “indiscriminate and reckless” cyber strikes that served “no legitimate national security interest”.
Cyber security consultant Andrew Tsonchev said individuals can get “caught up” in the attacks.
He said: “The more obvious and urgent effect that people need to be aware of is that the services they use – the essential services – are at risk and are actively being targeted for sabotage.”