"The recent attack is at an unprecedented level and will require a complex global investigation to identify the culprits", Europol said in a statement.
The attack is believed to be the biggest online extortion attack ever recorded.
Victims have paid about $30 000 in ransom so far, with the total expected to rise substantially next week, said Tom Robinson, chief operating officer and co-founder of Elliptic Enterprises, a ransomware consultant that works with banks and companies in the United Kingdom, the U.S. and Europe.
"The business sector invests heavily in cyber security and it is essential that the Department of Communications, Climate Action and Environment has adequate resources to address the related policy issues including the implementation of the Directive on Security of Network and Information Systems". The fact is the NHS has fallen victim to this.
He said it was too early to say who is behind the onslaught and what their motivation was.
Friday's attack was the latest in the growing menace of ransomware in which hackers deliver files to computers that automatically encrypt their data, making it unusable until a ransom is paid.
The effects were felt across the globe, with Russia's Interior Ministry and companies including Spain's Telefonica, FedEx Corp.in the USA and French carmaker Renault all reporting disruptions.
Students at universities in China were locked out of their work, including dissertations and thesis papers, according to Chinese media and reported by The Associated Press.
Nonetheless, the experts say such widespread attacks are tough to pull off. Microsoft swiftly released software "patches" to fix those holes, but many users still haven't installed updates or still use older versions of Windows.
The researcher tweeted that he initially didn't know that his actions would stop the malware.
"Or we could potentially see copycats mimic the delivery or exploit method they used", he said.
Officials across the globe scrambled over the weekend to catch the culprits behind a massive ransomware worm that disrupted operations at auto factories, hospitals, shops and schools, while Microsoft on Sunday pinned blame on the U.S. government for not disclosing more software vulnerabilities.
Microsoft said it had taken the "highly unusual step" of releasing a patch for computers running older operating systems including Windows XP, Windows 8 and Windows Server 2003.
Infected computers appear to largely be out-of-date devices that organizations deemed not worth the price of upgrading or, in some cases, machines involved in manufacturing or hospital functions that proved too hard to patch without possibly disrupting crucial operations, security experts said.
Meanwhile, an worldwide manhunt is under way to find those responsible for a massive global cyberattack that hit as many as 100 countries.
The attacks exploit a vulnerability in outdated versions of Microsoft Windows that is particularly problematic for corporations that don't automatically update their systems.
NHS Digital said it would take several weeks to restore some key equipment, such as MRI scanners, which run on the affected Windows XP programme.
That's why companies are anxious to beef up security or combat potential infections, according to Aviv Grafi, the chief technology officer of Votiro, another cybersecurity firm. "There are also a small number of reports made to the Australian Cybercrime Online Reporting Network that may be cases of this ransomware campaign, but these have yet to be confirmed". But, thanks to a security researcher at MalwareTech, the pace of the attack was slowed down.
The anonymous researcher, who goes by the name MalwareTech, warned the Wanna Decryptor ransomware that affected more than 100,000 systems across the world could just be the start. "They are processing a lot of sensitive data".
The software tools to create the attack were revealed in April among a trove of NSA spy tools that were either leaked or stolen.
British cybersecurity expert Graham Cluley doesn't want to blame the NSA for the attack.
Neema Singh Guliani, legislative counsel at the ACLU, said the ransomware attack raises questions about agencies stockpiling vulnerabilities instead of responsibly disclosing them.
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