Senior security staff held another meeting in the White House Situation Room on Saturday, and the Federal Bureau of Investigation and National Security Agency were trying to identify the perpetrators of the massive cyber attack, said the official, who spoke on condition on anonymity to the news agency to discuss internal deliberations.
"This means that as a new working week begins it is likely, in the United Kingdom and elsewhere, that further cases of ransomware may come to light, possibly at a significant scale", the NCSC said. "Today people will go to GP surgeries, we still don't know whether all GP surgeries across the country are going to be affected by this cyber security crisis or not, and we haven't had a dickie-bird from Jeremy Hunt".
If you have a hospital appointment you should still attend unless you are contacted and told not to.
"It is important to note that the vast majority of NHS organisations report that they are running contemporary IT systems, which are commissioned depending on local need", the NHS said in a statement.
A spokesman for the trust said: "Barts Health staff have been working tirelessly over the weekend, using tried and tested processes to keep patients safe and well cared for". 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.
Dr Anne Rainsberry, national incident director at NHS England, said: "There are encouraging signs that the situation is improving, with fewer hospitals having to divert patients from their A&E units".
The initial attack, known as "WannaCry", paralyzed computers that run Britain's hospital network, Germany's national railway and scores of other companies and government agencies worldwide in what was believed to be the biggest online extortion scheme so far.
"Most have found ways of working around this but seven, including Barts in London, have asked for extra support".
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The crematorium, he says, was established in Sednaya prison, north of Damascus, where political prisoners are held. A satellite image of Saydnaya prison released by the US State Department.
Brad Smith criticized U.S intelligence agencies, including the CIA and National Security Agency, for "stockpiling" software code that can be used by hackers.
"As cybercriminals become more sophisticated, there is simply no way for customers to protect themselves against threats unless they update their systems", Mr. Smith said.
"Otherwise they're literally fighting the problems of the present with tools from the past".
The apparent chink in the NHS's defences led to criticism of the Government, with the Liberal Democrats demanding an inquiry.
Japan's Chief Cabinet Secretary Yoshihide Suga said there weren't any concerns about damage in the country.
"The recent attack is at an unprecedented level and will require a complex global investigation to identify the culprits", the European police agency added.
"We've seen the extent to which the ransomware, which had its infection rates slowed down over the weekend, now mutated by the cyber crime groups behind it", Rob Wainwright, director of the European Union police agency Europol, told ITV News.