The NHS alone continues to run 70,000 devices using Windows XP, leaving an open goal for hackers to propagate their Wanna Decryptor ransomware across the hospital network.
But it is only estimated to have impacted at least eight businesses in Australia.
In Australia, Alistair MacGibbon, special advisor to Prime Minister Malcolm Turnbull on Cyber Security, said some small businesses would likely be hit "but as a whole of nation we can be confident, so far, that we have missed the worst of this".
"We weren't able to ingest the threat vector, which was probably an email that contained this malicious code in it, or a link to malicious code, and as a effect we were probably better protected than our European cousins". Companies including Hitachi and Nissan Motor Co. reported problems but said they said had not seriously affected their business operations.
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Australian cyber security minister Dan Tehan told Australian Broadcasting Corp radio: "At this stage, it does seem like that we have missed the major impact of this ransomware incident".
He said this latest attack was a reminder of the importance of good digital hygiene.
Speaking to Al Jazeera on Smith's post, Larry Magid, a technology journalist and CEO of ConnectSafely.org, said: "There is some speculation that this code was being stored in the NSA labs, potentially as a cyberweapon that the U.S. might have used against its own adversaries".
And more local computer systems are expected to be hit.
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However, under the Trump administration, relations have warmed and the USA is fully supporting Saudi Arabia in its regional role. Trump will be visiting Riyadh on Friday on his first worldwide trip as U.S. president.
This particular attack used malicious emails to encrypt a computer's data and demand payment of hundreds of dollars to decode the data.
MacGibbon said it was still not known how the virus had originated and then spread, although it was likely the transmission included email.
"We clearly don't advocate paying criminals, because we don't do it offline and we shouldn't be doing it online, and that's the best advice I can give", he said.
USA package delivery giant FedEx, European vehicle factories, Spanish telecoms giant Telefonica, Britain's health service and Germany's Deutsche Bahn rail network were among those hit. Spanish telco company Telefonica and USA delivery service FedEx have also admitted to being targeted.
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