The unprecedented global ransomware cyberattack has hit more than 200,000 victims in more than 150 countries, Europol executive director Rob Wainwright has said.
The head of the pan-European Union policing agency said that few had given in to the demands for payment to unblock files so far, but warned that the situation was escalating.
Wainwright said he was worried that the ransomware attack might spread further once people return to work on Monday and log on to their computers.
"We are running around 200 global operations against cyber crime each year but we've never seen anything like this," he told Britain's ITV television.
"The latest count is over 200,000 victims in at least 150 countries. Many of those victims will be businesses, including large corporations.
"The global reach is unprecedented."
He said the motivation remained unknown but ransomware attacks were normally "criminally minded".
"Remarkably few payments so far have been made, so most people are not paying this," Wainwright said.
"We're in the face of an escalating threat, the numbers are going up.
"I'm worried about how the numbers will continue to grow when people go to work and turn on their machines on Monday morning."
'Ooops' message, $300 ransom
Images appear on victims' screens demanding payment of $300 (275 euros) in the virtual currency Bitcoin, saying: "Ooops, your files have been encrypted!"
Payment is demanded within three days or the price is doubled, and if none is received within seven days the locked files will be deleted, according to the screen message.
Bitcoin, the world's most-used virtual currency, allows anonymous transactions via heavily encrypted codes.
Experts and governments alike warn against ceding to the demands and Wainwright said few victims so far had been paying up.
Security firm Digital Shadows said on Sunday that transactions totalling $32,000 had taken place through Bitcoin addresses used by the ransomware.
Banks, trains and automobiles, Universities and Hospitals.
Symantec said the majority of organisations affected were in Europe.
The companies and government agencies targeted were diverse.
Europol's Wainwright said few banks in Europe had been affected, having learned through the "painful experience of being the number one target of cyber crime" the value of having the latest cyber security in place.
Russia's interior ministry said some of its computers had been hit, while the country's banking system was also attacked, although no problems were detected, as was the railway system.
French carmaker Renault was forced to stop production at sites in France, Slovenia and Romania, while FedEx said it was "implementing remediation steps as quickly as possible".
Germany's rail operator Deutsche Bahn said its station display panels were affected.
Sky News reported Sunday that seven organisations which manage hospital care within England's National Health Service are continuing to divert patients from the emergency room, a figure which an NHS spokeswoman was not able to confirm to AFP.
Universities in China, Italy and Greece were also hit.
The US Treasury Department said it will play a "leading role" in protecting the global financial system's IT infrastructure.
