The only warning is a frozen computer screen.
Microsoft has blamed the United States government for creating the software code that was used by hackers to launch the cyber-attacks. And while Microsoft said it had already released a security update to patch the vulnerability one month earlier, the sequence of events fed speculation that the NSA hadn't told the us tech giant about the security risk until after it had been stolen.
In fact, reports already suggest that over 100 countries are being affected as the ransomware is spreading at an alarming rate. And the software is already inspiring imitators, as the Bleeping Computer site reports.
While the NSA has not commented on either the WannaCry attack or Microsoft's response, Tom Bossert, President Trump's Homeland Security advisor discussed at Monday's daily White House press briefing that the infection rate has been relatively low in the US compared to overseas infection rates, and that no federal systems have been compromised. Not decrypting files even after users have paid serves as a very salient lesson to anyone effected by ransomware that there is little benefit in paying the ransom.
But security minister Ben Wallace said the Government had put £1.2 billion into combating cyber attacks during the last strategic defence and security review, including a £50 million pot to support NHS IT networks. Security agencies in affected countries were racing to find out.
Attackers target users via an email phishing scam, according to the U.S. Computer Emergency Readiness Team.
Pankit Desai, co-founder and chief executive officer at cyber security start-up Sequretek, said India's unorganised sector may have escaped dire consequences so far, but the attack is ongoing. In Indonesia, the ransomware locked patient files on computers in two hospitals in the capital, Jakarta, causing delays.
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In India, 102 computer systems of the Andhra Pradesh police were hacked on Saturday and a Nissan Renault vehicle plant production was halted because of the malware. About 18 systems were hijacked an eventually disabled, the Business Standard reported. Because of the prevalence of older Microsoft operating systems there, up to 5 percent of computers affected globally could be in India.
The attack also proves how potentially risky massive computer disruptions can be.
A Nissan vehicle factory in the north-eastern city of Sunderland was also affected, a spokeswoman said.
Other Spanish firms to be hit included power firm Iberdrola and utility provider Gas Natural.
However staff beginning the working week have been told to be careful.
The auto manufacturer had to halt production at many sites, including in France, Slovenia and Romania, as part of measures to stop the spread of the virus. "How the hell did this get on there, and could this be repeatedly used again?" said Barlow. It said its plant at Douai in northern France would be back to normal on Tuesday, following checks. "They can do so much damage", he says.
Computers around the globe were hacked beginning last Friday using a security flaw in Microsoft's Windows XP operating system, an older version that was no longer given mainstream technical support by the U.S. computing giant. There were no reported cases in New Zealand.