European policing and security agencies said the fallout from a ransomware attack that has already crippled more than 200,000 computers around the world could deepen as people return for another work week.
Ransomware is a malicious software that blocks access to data on an affected computer until a ransom is paid and displays a message requesting payment to unlock it.
The effects were felt across the globe, with Russia's Interior Ministry and companies including Spain's Telefonica, FedEx Corp.in the US and French carmaker Renault all reporting disruptions.
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 canceled appointments and operations.
Chief executive Paul Hawkins said: "As a precautionary measure over the weekend a comprehensive programme of diagnostics and preventative work was carried out to protect our systems".
In China, "hundreds of thousands" of computers at almost 30,000 institutions and organizations were infected by late Saturday, according to Qihoo 360, one of China's largest providers of antivirus software.
Experts were urging organizations and companies to update older Microsoft operating systems immediately to limit vulnerability to a more powerful version of the malware - or to future versions that can't be stopped.
According to reports, ATMs or automated teller machines are highly vulnerable to such malware attacks as they now run on old version of Microsoft's Windows operating system, making a software security patch update a necessary exercise.
What isn't in question is that follow-up attacks based on something similar to WannaCrypt are likely and that systems therefore really need protecting.More news: Superhero Beat 'em Up Injustice 2 Gets Final Launch Trailer
Danish firm Heimdal Security warned on Sunday that the new Uiwix strain doesn't include a kill-switch domain, like the one that proved instrumental in minimising the harm caused by WannaCrypt last week, although this is subject to some dispute.
Computers running unpatched old operating systems, such as Windows XP, are particularly vulnerable.
"We haven't fully dodged this bullet at all until we're patched against the vulnerability itself", Kalember said.
Security firm Digital Shadows said on Sunday that transactions totaling $32,000 had taken place through Bitcoin addresses used by the ransomware.
The NHS, which was showcased in the opening ceremony of the 2012 Olympic Games, employs more than 1.5 million people, making it one of the world's biggest employers alongside the U.S. Department of Defence, Walmart and the People's Liberation Army of China.
The president of Microsoft laid some of the blame at the feet of the USA government.
Putin was referring to a weekend blog post by Microsoft president Brad Smith stating that the US National Security Agency had developed the code being used in the attack.
Jan Op Gen Oorth, spokesman for Europol, said the number of individuals who have fallen victim to the cyberextortion attack could be much higher. Security experts say this attack should wake up every corporate board room and legislative chamber around the globe.