The ransomware in question, WannaCry, relies on a flaw in the Windows 10 code for which Microsoft issued a patch on March 14.
At least one strain of the ransomware has proven especially vicious.
The ransomware also generates random IP addresses not limited to local networks, which means WannaCry may also be able to spread online if websites allow NetBIOS packets from outside networks, according to McAfee researchers. "There is this stream of liability that flows from the ransomware attack", he said.
Recovering from the virus could cost businesses billions of dollars as they try to become operational once more.
The attack, known as "WannaCry" had a major impact across Asia as workers there returned to work on Monday, with Chinese state media saying nearly 30,000 institutions there had been infected.
Labour's shadow health secretary, Jonathan Ashworth, in a letter to Health Secretary Jeremy Hunt, said concerns were repeatedly flagged about outdated computer systems.
Colleges: Internet security firm Qihoo360 issued a "red alert" over the weekend, saying a large number of colleges and students in China had been hit by the ransomware attack.
Deutsche Bahn: The German railway company told CNNMoney that due to the attack "passenger information displays in some stations were inoperative" as were "some ticket machines".
Cybersecurity experts say the worm affects computers using Microsoft operating systems and takes advantage of a vulnerability in the software to spread the infection.
Russia's central bank said Saturday that no incidents had "compromising the data resources" of Russian banks, state news agency Tass reported.
Reuters/Shannon StapletonA Microsoft logo is seen at a pop-up site for the new Windows 10 operating system at Roosevelt Field in Garden City, New York.
He said tech companies, customers and the government need to "work together" to protect against attacks.
Interior Ministry: The Russian Interior Ministry acknowledged a ransomware attack on its computers, adding that less than 1% of computers were affected.
Megafon: A spokesperson for Russian telecommunications company Megafon told CNN that the cyberattack affected call centers but not the company's networks.
"A customer who pairs a Windows Mixed Reality headset with motion controllers will have a rich and immersive experience across creativity tools, productivity, games, and entertainment", Myerson said. National Health Service, but it doesn't help computers already infected by the virus.
Telefónica, a Spain-based telecommunications company, was among the first major organizations to report being hit by the attack, and institutions in England's health care sector first reported problems by late morning on Friday, according to the FT. "At this stage, we do not have any evidence that patient data has been accessed".
"I'm anxious about how the numbers will continue to grow when people go to work and turn on their machines on Monday", he said.
Britain's National Health Service said about a fifth of NHS trusts - the regional bodies that run hospitals and clinics - were hit by the attack on Friday, leading to thousands of cancelled appointments and operations.