That's why it's called ransomware. A British security researcher was able to put a temporary stop to it, heavily decreasing its virality, but the WannaCry threat isn't gone and will affect more Windows users on Monday as they return to work.
Australia appears to have escaped the worst fallout from a huge global ransomware attack, but the Prime Minister's cybersecurity adviser has warned that "this is not game over" in the battle between hackers and security agencies.
It was among a large number of hacking tools and other files that a group known as the Shadow Brokers released on the Internet. While Microsoft had released an update in March with a patch to address the problem, any computers that had not yet installed that update were vulnerable to attack. The malware is targeting Microsoft's Windows operating systems.
The world is facing the most unsafe cyberattack it ever had to deal with so far, and it's an attack that it can't be stopped entirely for the time being. It has hit Telefonica in Spain, FedEx in the U.S and the National Health Service in the UK.
Seven hospitals remained on A&E divert on Sunday afternoon, with ambulances taking emergency patients elsewhere.
Also hit were Deutsche Bahn, the Russian Central Bank, Russian Railways, Russia's Interior Ministry, Megafon and Telefónica. The ATMs have been taken offline, and those who come to withdraw money see a window showing that the files on the system have been encrypted, along with a demand for the bitcoin transaction.
The world's biggest ransomware attack strikes hundreds of thousands of computers worldwide.More news: Trump says NAFTA pull-out would shock system
The malware, using a technique purportedly stolen from the US National Security Agency, stopped care Friday at hospitals across the United Kingdom, affected Russia's Ministry of Interior and infected company computer systems in countries from Eastern Europe to the US and Asia. Install Microsoft's patch. 3. Speaking on the BBC's Andrew Marr Show, Fallon said the Vanguard submarines that carry the deterrent "operate in isolation" when on patrol, implying that they can't be hacked remotely.
Two researchers in their 20's had halted the ransomeware attack on Saturday after discovering and activating the software's "kill switch".
There are different variants of what happens: Other forms of ransomware execute programs that can lock your computer entirely, only showing a message to make payment in order to log in again.
"The whole idea of ransomware is for it to get its hands on every file it can find and encrypt it, so if you can just wipe your machine and restore from a backup, then it's not an issue", he says.
Computers and networks that hadn't recently updated their systems are still at risk because the ransomware is lurking. People are anxious a second wave of cyberattacks could strike around the world on Monday as employees return to their desks and log onto their computers.
Despite cyber security experts working hard to save hospitals from the attack, it may turn out to be far worse than previously thought after the weekend.
"And also existing known infections can spread, we can't say what scale the new cases will occur at but it's likely there will be some".