Of the 48 affected NHS England hospitals, six remain unoperational

This attack most likely occurred because some hospitals and other affected organizations may not have applied a patch that Microsoft released or were using outdated operating systems that the software giant no longer supports, Woodward said.

Telecommunications company Telefonica was among many targets in Spain. He said the situation was under control.

The prime minister's right-hand man on cyber security, Alastair MacGibbon, is working with officials and health agencies to determine any impact on Australia. The number of individual strikes totals more than 75,000, according to cybersecurity firm Avast.

No one has claimed responsibility for the cyber attack, which by Saturday had begun to subside after an unidentified British researcher who tweets at @MalwareTechBlog reportedly activated a "kill switch", a code built into the ransomware that provided a way of stopping the attack.

The malware's name is WCry, but analysts were also using variants such as WannaCry.

The Scottish Government said other public bodies are running checks on their systems as a precaution ahead of the start of the working week. "We are implementing remediation steps as quickly as possible", a statement said.

Britain's National Cyber Security Center says teams are working "round the clock" to restore hospital computer systems after a global cyberattack that hit dozens of countries forced British hospitals to cancel and delay treatment for patients.

In Spain, major firms including Telefonica were hit, with employees told to shut down workstations immediately through megaphone announcements. No information about the attackers has been released. Two security firms - Kaspersky Lab and Avast - said they had identified the malicious software behind the attack in over 70 countries, although both said the attack had hit Russian Federation the hardest.

He urged Windows users to update their systems and reboot. The effects of the attack on Turkey is unclear. "We will continue to work with affected (organizations) to confirm this", the agency said.

These hackers "have caused enormous amounts of disruption- probably the biggest ransomware cyberattack in history", said Graham Cluley, a veteran of the anti-virus industry in Oxford, England.

Russian Central Bank: State media agency Tass reported the bank discovered malware bulk emails to banks but detected no compromise of resources. The company announced on Saturday that it was reversing that policy.

A spokeswoman for the company did not say how many sites were affected by the shutdown, which "was one of the measures taken to stop the virus from spreading". "This is not targeted at the NHS".

"We are aware that a number of NHS organisations have reported that they have suffered from a ransomware attack".

"These attacks underscore the fact that vulnerabilities will be exploited not just by our security agencies, but by hackers and criminals around the world", Mr Patrick Toomey, a staff attorney with the American Civil Liberties Union, said in a statement. But it appears to be "low-level" stuff, Eisen said Saturday, given the amount of ransom demanded - $300 at first, rising to $600 before it destroys files hours later. It appeared as if they had been deleted, he said. That cheap move redirected the attacks to MalwareTech's server, which operates as a "sinkhole" to keep malware from escaping.

"The ransomware can spread without anyone opening an email or clicking on a link".

"Ransomware becomes particularly nasty when it infects institutions like hospitals, where it can put people's lives in danger", said Kroustek, the Avast analyst.

"This attack was not specifically targeted at the NHS and is affecting organisations from across a range of sectors", NHS Digital, the computer arm of the health service, said in a statement.

The cyberattack was initially believed to target only hospitals in the United Kingdom, but it turned out to be a worldwide attack, British Prime Minister Theresa May said.

Barts officials had to cancel routine appointments and divert ambulances to neighboring hospitals, they said, adding that the switchboard at Newham University Hospital also was affected.

At two London hospitals, a British medical student found widespread computer issues, he told CNN.

Caroline Brennan, 41, went to the hospital to see her brother, who had open heart surgery. "Because they could have done something ages ago to get this problem fixed, and they didn't do it".

He says "today, it happened to 10,000 computers. there's no barrier to do it tomorrow to 100 million computers".

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