International investigators hunted for those behind an unprecedented cyber attack that affected systems in dozens of countries, including at banks, hospitals and government agencies, as security experts sought to contain the fallout.
The assault, which began on Friday and was being described as the biggest-ever cyber ransom attack, struck state agencies and major companies around the world — from Russian banks and British hospitals to FedEx and European car factories.
"The recent attack is at an unprecedented level and will require a complex international investigation to identify the culprits," said Europol, Europe's police agency.
Europol said a special task force at its European Cybercrime Centre was "specially designed to assist in such investigations and will play an important role in supporting the investigation".
The attacks used ransomware that apparently exploited a security flaw in Microsoft operating systems, locking users' files unless they pay the attackers a designated sum in the virtual currency Bitcoin.
But experts and government alike warn against ceding to the hackers' demands.
"Paying the ransom does not guarantee the encrypted files will be released," the US Department of Homeland Security's computer emergency response team said.
"It only guarantees that the malicious actors receive the victim's money, and in some cases, their banking information."
How they did it
Images appeared on victims' screens demanding payment of $300 in 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 files will be deleted, according to the screen message.
150 Number of countries hit
02 L Number of people affected