A cybersecurity researcher has been credited with slowing the ransomware after accidentally discovering a "kill switch" that could prevent the spread.
The 22-year-old Britain-based researcher, identified online only as MalwareTech, explained Saturday that he spotted a hidden web address in the "WannaCry" code and made it official by registering its domain name.
Several European countries, including Russian Federation, were among the worst hit in the attack.
A United Kingdom report says a young cyber security researcher has been credited with helping to halt the spread of the global ransomware cyber-attack by accidentally activating a so-called "kill switch" in the malicious software. But many companies and individuals haven't installed the fixes yet or are using older versions of Windows that Microsoft no longer supports and didn't fix.
The widescale attack involved ransomware, in which infiltrated computers are held hostage until a ransom is paid, in conjunction with "a worm functionality" that automatically spread the virus across global networks.
The most disruptive attacks were reported in the United Kingdom, where hospitals and clinics were forced to turn away patients after losing access to computers.
Cyber security experts say many companies may be affected, but won't find out until they reopen for business tomorrow morning.
Now that this "WannaCry" malware is out there, the world's computer systems are vulnerable to a degree they haven't been before, unless people everywhere move quickly to install Microsoft's security patches.
As terrifying as the unprecedented global "ransomware" attack was, cybersecurity experts say it's nothing compared to what might be coming - especially if companies, organizations and governments don't make major fixes.
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Huss and others were calling MalwareTech a hero on Saturday, with Huss adding that the global cybersecurity community was working "as a team" to stop the infections from spreading.
Those attacks require a serious worldwide investigation for identifying the hackers, pointed also the Agency.
It was believed to the biggest attack of its kind ever recorded.
It said that train services were not disrupted but some electronic boards at stations announcing arrivals and departures had been affected.
The head of Turkey's Information and Communication Technologies Authority or BTK said the nation was among those affected by the ransomware attack.
"Do not open emails from unknown sources or containing suspicious links or attachments. The work to eliminate it and upgrade anti-virus protection is now underway", they said in an official statement.
What occurred was an "indiscriminate attack across the world on multiple industries and services", Mr Wainwright said, including Germany's rail network Deutsche Bahn, Spanish telecommunications operator Telefonica, US logistics giant FedEx and Russia's interior ministry.
NY [U.S.], May 14: The World's biggest cyber attack which has hit 200,000 victims in at least 150 countries threatens to create more havoc on Monday when people return to work.
Researchers with security software maker Avast said they had observed 57,000 infections in 99 countries, with Russia, Ukraine and Taiwan the top targets.
NHS Digital said that 4.7 per cent of devices within the NHS use Windows XP, with the figure continuing to decrease.