Some of the first reports emerged from England, where hospitals across the country were hit by ransomware attacks, in which hackers infect computers with malicious software and demand ransoms to restore access, according to the National Health Service (NHS).
NHS services across England and Scotland have been hit by a large-scale cyber-attack.
Many researchers say the incidents appear to be linked, but say it may not be a coordinated attack on specific targets, BBC News reported.
A report from a security firm indicates more than 45,000 malicious computer attacks in 74 countries in the past 10 hours.
Russia's Interior Ministry released a statement acknowledging a ransomware attack on its computers, adding that less than 1% of computers were affected, and that the virus is now "localized".
Pictures posted on social media showed screens of NHS computers with images demanding payment of 300 U.S. dollars worth of the online currency Bitcoin, threatening to delete files within seven days. Prime Minister Theresa May issued a statement on the attack, declaring that no patient data is believed to have been compromised.
Hospitals in areas across Britain found themselves without access to their computers or phone systems.
An IT worker at the public health care system tells The Guardian newspaper that it's the biggest problem they've seen in their six years working for the service. Still, the news prompted security teams at large financial services firms and businesses around the world to review their plans for defending against ransomware attacks, according to executives with private cyber security firms.
Reports in Russian Federation say the nation's top criminal investigation agency, the Investigative Committee, has also been targeted.
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Among the many other institutions that were affected were hospitals and telecommunications companies across Europe, Russia, Asia and beyond, according to MalwareHunterTeam, a security firm that tracks ransomware attacks. Computers were locked up and users' files held for ransom when dozens of countries were hit in a cyberextortion attack that targeted hospitals, companies and government agencies.
Hospital emergency rooms said only the most serious cases could be handled, surgical operations had to be cancelled, and thousands of health staff were unable to access vital patient information.
The National Cyber Security Centre (NCSC) was "working closely" with the NHS and that they will protect patient safety.
At least 16 organisations within the NHS, some of them responsible for several hospitals each, reported being targeted in today's hack. They said the system was down and that they can not transfer anyone till the computer system was back up so he is still in the theatre.
Derbyshire Healthcare NHS Trust said it had not been affected by the attack, but had switched off its IT systems.
The emergencies ministry told Russian news agencies it had repelled the cyberattacks while Sberbank said its cyber security systems had prevented viruses from entering its systems.
A statement released by Colchester General Hospital said: "On Friday the trust experienced a major IT problem, believed to have been caused by the cyberattack".
Krishna Chinthapalli, a doctor at Britain's National Hospital for Neurology & Neurosurgery who wrote a paper on cybersecurity for the British Medical Journal, warned that British hospitals' old operating systems and store of confidential patient information made them an ideal target for blackmailers.
"Looking at the trends, it was going to happen", he said.
Spain's Ministry of Energy, Tourism and Digital Agenda confirms the intrusion, describing it as "punctual attacks".