U.S. package delivery giant FedEx, European vehicle factories, Spanish telecoms giant Telefonica, Britain's health service and Germany's Deutsche Bahn rail network were among those hit.
More than 200,000 victims in around 150 countries have been infected by the ransomware which originated in the United Kingdom and Spain on Friday before spreading globally.
The attack involved a malware called Wanna Decryptor, which encrypts files on a user's computer, blocking them from view and demanding a payment to release them.
A devastating attack in December disabled thousands of computers across multiple government ministries in Saudi Arabia, and brought back memories of a similar attack on the country's flagship oil company Aramco in 2012.
Others have made a similar point: "While GCHQ can not be blamed for the NHS's reliance on out of date software, the decision that the NSA and GCHQ have made in keeping this vulnerability secret, rather than trying to get it fixed, means they have a significant share of the blame for the current NHS ransom", said the Open Rights Group.
Microsoft released patches last month and on Friday to fix a vulnerability that allowed the worm to spread across networks, a rare and powerful feature that caused infections to surge on Friday.
Friday's ransomware attack hit over 125,000 computer systems, with 48 National Health Service (NHS) trusts having to cancel appointment and operations.
Meanwhile Europol's chief told the BBC that that the ransomware was created to allow "infection of one computer to quickly spread across the networks", adding: "That's why we're seeing these numbers increasing all the time".
The anonymous specialist, known only as MalwareTech, issued a warning that hackers could upgrade the virus to remove the kill switch.
"In particular, making sure that our data is properly backed up and making sure that we are using the software patches, the anti-virus patches, that are sent out regularly by manufacturers".
Mr Wallace said it was a "red herring" to focus exclusively on the Windows XP operating system as being vulnerable, saying the virus had also attacked both Windows 7 and 8.1. The tool is called WCRYSLAP and can be found here.
The real damage caused by the nightmare that is the WannaCry malware is becoming clearer in the cold light of day. Do not give people any more access to your system than they need to do their job.
Though the worm is primarily affecting business, individuals with PCs running Windows should still take a few precautions.
Asked why a £5 million contract with Microsoft to protect the XP machines had been terminated, the spokesman said £50 million had been made available to NHS bodies for cyber security in the 2015 spending review.
The exploit can penetrate into machines that are now running unpatched version of Windows through 2008 R2 by exploiting flaws in Microsoft Windows SMB Server.
If you don't already have a backup routine, start now: Regularly save copies of all your files.
Also, be suspicious of uninvited documents that you receive through email.
Finally, always stay alert.
The virus is usually covertly installed on to computers by being hidden within innocent-looking emails containing links, which users are tricked into opening.
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