A number of organizations across the world have been hit by so-called ransomware cyber attacks.
Organizations in several countries, including Britain, the United States, China, Russia, Spain, Italy, Vietnam and Taiwan, reported on Friday that they had been attacked by a malicious software known as ransomware that locks up computers and demands a payment in Bitcoin to restore access.
It was not immediately clear whether the attacks were related to each other.
One cyber-security researcher said on his Twitter account that he had detected 36,000 instances of ransomware, called WannaCry and variants of that name, adding, "This is huge."
In the UK, the National Health Service (NHS) staff shared online screenshots of the WannaCry program as the state-run health service was hit by the cyber attack.
Russia's Interior Ministry said some of its computers were also hit by a "virus attack".
"The virus has been localized. Technical work is under way to destroy it and renew the means of virus protection," the ministry's spokeswoman, Irina Volk, was quoted as saying by Russian news agencies on Friday night.
Volk went on to say that some 1,000 computers -- less than one percent of their total number -- had been affected.
The malware also affected several companies in Spain with Telecoms giant Telefonica saying that it was aware of a "cyber-security incident."
However, it said the attacks had not affected clients and services.
Staff at Power firm Iberdrola and utility provider Gas Natural were told to turn off their computers as the firms had also been infected with ransomware.
Bitcoin wallets seemingly associated with ransomware were reported to have already begun filling up with cash.
Security architect Kevin Beaumont said, "This is a major cyber attack, impacting organizations across Europe at a scale I've never seen before."
The version of ransomware that appeared today is a new variant, the security firm Check Point said.
Aatish Pattni, the head of threat prevention for northern Europe at the security firm, said, "Even so, it's spreading fast."