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.
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.
The NCSC said it has assessed "with high confidence" that the GRU was "almost certainly responsible" for the 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".
What is the GRU accused of?
The NCSC says hackers from the GRU, operating under a dozen different names - including Fancy Bear - targeted:
The systems database of the Montreal-based World Anti-Doping Agency (Wada), using phishing to gain passwords. A group accessed athletes' data, which was later published
The Democratic National Committee in 2016, when emails and chats were obtained and subsequently published online. The US authorities have already linked this to Russia
Ukraine's Kyiv metro and Odessa airport, Russia's central bank, and two privately-owned Russian media outlets - Fontanka.ru and news agency Interfax - in October 2017. They used ransomware to encrypt the contents of a computer and demand payment
An unnamed small UK-based TV station between July and August 2015, when multiple email accounts were accessed and content stolen
What has the UK government said?
"The GRU's actions are reckless and indiscriminate: they try to undermine and interfere in elections in other countries; they are even prepared to damage Russian companies and Russian citizens," said Foreign Secretary Jeremy Hunt.
"This pattern of behaviour demonstrates their desire to operate without regard to international law or established norms and to do so with a feeling of impunity and without consequences.
"Our message is clear: together with our allies, we will expose and respond to the GRU's attempts to undermine international stability."
Do other countries carry out cyber attacks?
Russia is not the only state to have been accused of cyber attacks.
The UK blamed the Wannacry ransomware incident on North Korean actors in December 2017, as did the US, Australian, Canada, New Zealand, Denmark and Japan
In March this year, Britain blamed a campaign targeting universities around the world, including in the UK, on the Mabna Institute based in Iran
China-based groups linked to the state were accused of hacking UK think tanks last year by a US cyber-security company which investigated
In April, the UK said it had conducted a "major offensive cyber-campaign" against the Islamic State group