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He told the BBC the act was "unprecedented in its scale" and warned more people could find themselves affected on Monday morning. He added that the agency is still analyzing the virus and has yet to identify who is responsible for the attack.
The cyberattack has hit 200,000 computers in more than 150 countries, according to Rob Wainwright, executive director of Europol, the European Union's police agency.
This, he said, was allowing the "infection of one computer to quickly spread across the networks".
The WannaCry ransomware hit vulnerable Windows systems across the world with security experts estimating the affected systems could range between 100,000 and 200,000. It locks users out of their systems until they pay the crooks who installed it.
South Korea has been mostly spared from the global cyber chaos that crippled scores of governments and companies in 150 countries. Cybersecurity experts have said the majority of the attacks targeted Russia, Ukraine and Taiwan.
Many workers, particularly in Asia, had logged off on Friday before the malicious software, stolen from the US government, began proliferating across computer systems around the world. So far, he said, not many people have paid the ransom demanded by the malware.
"The numbers are still going up", Wainwright said. The virus took control of users' files and demanded $300 (£230) payments to restore access.
Microsoft posted an official notice on its site regarding the update as well as general guidance regarding the WannaCrypt attack. This one worked because of a "perfect storm" of conditions, including a known and highly risky security hole in Microsoft Windows, tardy users who didn't apply Microsoft's March software fix, and malware created to spread quickly once inside university, business and government networks. It seems to affect server software on organizations' networked computers.
The latest virus attack last week exploits a flaw in a version of Microsoft Windows first identified by United States intelligence. Machines that contained the patch are much less at risk than those that didn't.
But on Monday South Korea said just nine cases of ransomware had been found, giving no further details.
He said tech companies, customers and the government need to "work together" to protect against attacks.
The NHS was among hundreds of organisations affected around the world, with 47 trusts hit.
"There hasn't been any significant damage for us and our agencies, banks or healthcare system", Putin said.
Another government security official said no government systems were affected. Use it. And install updates for your other software, including apps. "Repeatedly, exploits in the hands of governments have leaked into the public domain and caused widespread damage". Here's how to turn automatic updates on.
The tool, known as "WannaCry", was stolen by a group known as the Shadow Brokers, using a weaponized Microsoft vulnerability developed by the NSA against the warnings of cyber security experts.