The U.K.'s National Cyber Security Center said it is "working round the clock" to restore vital health services.
All told, several cybersecurity firms said they had identified the malicious software, which so far has been responsible for tens of thousands of attacks, in more than 60 countries. It may have saved governments and companies millions of dollars and slowed the outbreak before USA -based computers were more widely infected.
"Like many other companies, FedEx is experiencing interference with some of our Windows-based systems caused by malware", said a spokesperson in a statement. "We are implementing remediation steps as quickly as possible".
Hospitals across Britain found themselves without access to their computers or phone systems.
Home Secretary Amber Rudd, who is to chair an emergency COBRA meeting to discuss the crisis later, could not confirm if all patient files had been backed up. There were also reports that the powerful Investigative Committee, which investigates high-level crime, and several other telecommunications companies had been targeted. Doctors' practices and pharmacies reported similar problems. Hospitals, with their often outdated IT systems and trove of confidential patient data, are a particularly tempting target.
Britain's home secretary says about one in five National Health Service trusts have been hit by the worldwide ransomware cyberattack, and that all but six are now back to normal. By Friday evening, the ministry said it had "contained" the attack and denied that any of its information had been stolen.
This is already believed to be the biggest online extortion attack ever recorded, disrupting services in nations as diverse as the U.S., Ukraine, Brazil, Spain and India.
This malware locks the system by encrypting the computer data and a message is shown on the monitor that the system could only be used when $300 paid.
Alan Woodward, visiting professor of computing at the University of Surrey, said there was evidence the ransomware was spreading using a Microsoft flaw exposed in a recent leak of information from US intelligence agencies.
Microsoft released a patch to fix the problem in March, but computer systems that did not install the update remain vulnerable.
Chris Wysopal of the software security firm Veracode said criminal organizations probably were behind the attack, given how quickly the malware spread.
"This was not an attack that targeted the NHS", British Prime Minister Theresa May said.
"For so many organisations in the same day to be hit, this is unprecedented", he said.
Spain, meanwhile, activated a special protocol to protect critical infrastructure in response to the "massive infection" of personal and corporate computers in ransomware attacks.
On Saturday, it was still unclear who was behind the sophisticated attack, which spread rapidly via email.
The Spanish government said several companies had been targeted in ransomware cyberattack that affected the Windows operating system of employees' computers. Targets were sent an encrypted, compressed file that, once loaded, allowed the ransomware to infiltrate the quarry's systems.
Elsewhere in Europe, the attack hit companies including Spain's Telefonica, a global broadband and telecommunications company. The attack froze computers at hospitals across the country, with some canceling all routine procedures.
Patrick Ward, a 47-year-old sales director, said his heart operation, which was scheduled for Friday, was cancelled at St. Bartholomew's Hospital in London.
Patients have reported being turned away, while some are stuck at hospital without access to discharge data.
TMT post, a Chinese online news outlet focusing on the Internet industry, reported that a number of Chinese universities had been affected by the attack. "It's stressful enough for someone going through recovery or treatment for cancer". The National Cyber Security Centre said it had detected 188 "high-level" attacks in just three months.
This is screengrab taken from the website of the East and North Hertfordshire NHS trust as Britain's National Health Service is investigating "an issue with IT" Friday May 12, 2017.
Former assistant attorney general for national security John Carlin joins Hari Sreenivasan for more on the attack.disabled3000869520zrSXZxrFf6Efalse215836215844http://www.pbs.org/newshour/bb/world-powers-look-djibouti-trade-military-access/World powers look to Djibouti for trade, military accessDjibouti, a tiny country in Northeast Africa, is situated at the gateway to the Suez Canal, one of the world's busiest shipping routes.