A massive cyber attack that was earlier reported to have hit the UK's National Health Service across England and Scotland has now proved to be of global scale, leveraging hacking tools believed to have been developed by the US National Security Agency.
The malware attack has infected tens of thousands of computers in nearly 100 countries, disrupting Britain's health system and global shipper FedEx among others.
Cyber extortionists seek to trick victims into opening malicious malware attachments to spam emails that appeared to contain invoices, job offers, security warnings and other legitimate files.
The ransomware encrypted data on the computers, demanding payments of $300 to $600 to restore access. According to Reuters, security researchers said they observed some victims paying via the digital currency bitcoin, though they did not know what percent had given in to the extortionists.
Researchers with security software maker Avast said they had observed 57,000 infections in 99 countries, with Russia, Ukraine and Taiwan the top targets.
Asian countries reported no major breaches till today, but officials in the region were scrambling to check and the full extent of the damage may not be known for some time.
China's official Xinhua news agency said some secondary schools and universities had been affected, without specifying how many or identifying them.
The most disruptive attacks were reported in Britain, where hospitals and clinics were forced to turn away patients after losing access to computers on Friday. Prime Minister Theresa May had said then it was part of a wider attack affecting organisations around the world (See: Massive malware attack hits UK's NHS; services disrupted)
International shipper FedEx Corp said some of its Windows computers were also infected. "We are implementing remediation steps as quickly as possible," it said in a statement.
Only a small number of US-headquartered organizations were hit because the hackers appear to have begun the campaign by targeting organizations in Europe, Vikram Thakur, research manager with security software maker Symantec, told Reuters today.
By the time they turned their attention to the United States, spam filters had identified the new threat and flagged the ransomware-laden emails as malicious, he added.
Infections of the worm appeared to have fallen off significantly after a security researcher bought a domain that the malware was connecting to, by chance undermining the malware's effectiveness.
Making the domain active appears to have stunted the spread of the worm, Thakur said.
"The numbers are extremely low and coming down fast," he said, while cautioning that any change in the original code could lead the worm to flare up again.
The US Department of Homeland Security said late on Friday it was aware of reports of the ransomware, was sharing information with domestic and foreign partners and was ready to lend technical support.
Telecommunications company Telefonica was among many targets in Spain, though it said the attack was limited to some computers on an internal network and had not affected clients or services. Portugal Telecom and Telefonica Argentina both said they were also targeted.
Private security firms identified the ransomware as a new variant of "WannaCry" that had the ability to automatically spread across large networks by exploiting a known bug in Microsoft's Windows operating system.
The hackers, who have not come forward to claim responsibility or otherwise been identified, likely made it a "worm", or self spreading malware, by exploiting a piece of NSA code known as "Eternal Blue" that was released last month by a group known as the Shadow Brokers, researchers with several private cyber security firms said.
"This is one of the largest global ransomware attacks the cyber community has ever seen," said Rich Barger, director of threat research with Splunk, one of the firms that linked WannaCry to the NSA.
The Shadow Brokers released Eternal Blue as part of a trove of hacking tools that they said belonged to the US spy agency.
Microsoft said it was pushing out automatic Windows updates to defend clients from WannaCry. It issued a patch on 14 March to protect them from Eternal Blue.
"Today our engineers added detection and protection against new malicious software known as Ransom:Win32.WannaCrypt," Microsoft said in a statement on Friday, adding it was working with customers to provide additional assistance.
On Wednesday, hackers disrupted the websites of several French media companies and aerospace giant Airbus. Also, the hack happened four weeks before a British general election in which national security and the management of the state-run National Health Service (NHS) are important issues.
Authorities in Britain have been braced for cyber attacks in the run-up to the vote, as happened during last year's US election and on the eve of the French vote.
On Friday, Russia's interior and emergencies ministries, as well as its biggest bank, Sberbank, said they were targeted. The interior ministry said on its website that about 1,000 computers had been infected but it had localized the virus.
The emergencies ministry told Russian news agencies it had repelled the cyber attacks while Sberbank said its cyber security systems had prevented viruses from entering its systems.