Dozens of countries hit by huge cyberextortion attack, including US

"We are taking immediate steps to minimize the impact of the attack across NHS Scotland and restrict any disruption", it added.

WannaCry is a form of "ransomware" that locks up the files on your computer and encrypts them in a way that you can not access them anymore.

Cybersecurity experts told ABC News that the unidentified attackers exploited a vulnerability in Microsoft Windows that was identified by the U.S. National Security Agency (NSA) and leaked to the public by the hacker group The Shadow Brokers in April.

The US Department of Homeland Security said late on Friday that it was aware of reports of the ransomware, was sharing information with domestic and foreign partners and was ready to lend technical support.

At least 16 National Health Service-related organizations were affected, officials said, although patients' medical information did not appear to be compromised.

British based cyber researcher Chris Doman of AlienVault said the ransomware "looks to be targeting a wide range of countries", with initial evidence of infections in at least two dozen nations according to experts from three security firms.

Hackers exploiting data stolen from the U.S. government conducted extensive cyberattacks on Friday that hit dozens of countries around the world, severely disrupting Britain's public health system and causing havoc in tens of thousands of computers elsewhere.

On Twitter, whistleblower Edward Snowden blamed the NSA.

Britain's National Cyber Security Centre, part of the GCHQ spy agency, said it was aware of a cyber incident and was working with NHS Digital and the police to investigate.

He said hospitals affected by today's attack - which is on an unprecedented scale - might choose to pay the hackers to release their computers, as had happened in the past.

Hospitals, health clinics, family doctor surgeries across England and Scotland were seriously affected by what was the biggest ever attack on the NHS.

Britain's National Health Service is a source of pride for many Britons but faces substantial budget issues and has had previous problems with its huge IT system.

The interior ministry said on its website that around 1,000 computers had been infected but it had localised the virus.

NHS Digital, which oversees hospital cybersecurity, says the attack used the Wanna Decryptor variant of malware, which infects and locks computers while the attackers demand a ransom.

"Papworth hospital [in Cambridgeshire] was attacked and the head of IT there said they were lucky because they had backed up the data just a few minutes before", he said. Russian Federation appeared to be the hardest hit, according to security experts, with the country's Interior Ministry confirming it was struck.

The Spanish government said several companies had been targeted in ransomware cyberattack that affected the Windows operating system of employees' computers.

IT specialists were working to resolve the problem as quickly as possible, a statement from the NHS Trust said.

Spain's Telefonica was among the companies hit. "And some of them may not be well prepared for such attacks", Camacho said.

A spokesperson for FedEx confirmed to ABC News that the company is among the victims of the ransomware attacks.

Iberdrola and Gas Natural, along with Vodafone's unit in Spain, asked staff to turn off computers or cut off internet access in case they had been compromised, representatives from the firms said.