NHS Digital said the NHS itself was not specifically the target of the attack but part of a wider "Wanna Decryptor" ransomware campaign.
"The investigation is at an early stage but we believe the malware variant is Wanna Decryptor", the NHS said in a statement.
A number of English hospitals have been hit by a suspected large scale cyber attack, the NHS has confirmed.
The hackers behind the "ransomware" attack were demanding $300 worth of the online currency Bitcoin to release files from encryption, the Mirror and the Telegraph reported. The only people suffering are people that need emergency care.
The NHS said 16 of its organisations - some containing several hospitals - have been affected.
"We are also in contact with the National Services Centre who are co-ordinating the situation on behalf of NHS Scotland. We have activated our major incident plan to make sure we can maintain the safety and welfare of patients", said Barts in a statement. Having to cancel appointments and close entire hospitals is devastating for the industry. It warns that the ransom demand will double after three days and that after seven days, "you won't be able to recover your files forever".
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The victims included Telefonica, the nation's biggest telecommunications firm, while other Spanish firms such as power company Iberdrola and utility Gas Natural took preventive measures. It exploits a vulnerability in Microsoft's Windows operating system that allows it to automatically spread across networks, which gives it the ability to quickly infect large numbers of machines at the same organization.
NHS trust IT systems in London, Blackburn, Nottingham, Cumbria and Hertfordshire have also reportedly been affected.
In the United Kingdom, hospitals in London, northwest England and other parts of the country reported problems and asked patients not to come to the hospitals unless it was an emergency.
The most worrying development was the problems with the hospital's referral system, Sean said.
The National Cyber Security Center, an arm of the GCHQ, the British electronic surveillance agency, said it was investigating the incident. The cyberattack, he said, could cause a major backlog in referrals.
Jamie Moles, Principal Security Consultant at Lastline said: "Interestingly, the NHS takes a very strict and sanitary approach to dealing with these attacks, shutting down nearly all of its IT capabilities while it triages and treats the problem".
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