Experts advise people not to pay, as it would only encourage the attackers, there is no guarantee that they will unblock files, and may result in them gaining access to victims' bank details.
Edward Snowden, the whistleblower who exposed the broad scope of NSA surveillance in 2013, tweeted, "If @NSAGov had privately disclosed the flaw used to attack hospitals when they *found* it, not when they lost it, this may not have happened". Users should also install security updates on their computers and back up their files to avoid losing them in case of an attack.
Friday's cyber attack hit 200,000 victims in at least 150 countries, the head of the European Union's police agency said on Sunday, adding he feared that number would grow when people return to work on Monday.
"We're not talking about a government organisation or a hospital or anything like that".
The majority of the attacks targeted Russia, Ukraine and Taiwan.
"I think it is concerning that we could definitely see a similar attack occur, maybe in the next 24 to 48 hours or maybe in the next week or two", Huss said. "We've seen huge investments cuts in the infrastructure of the NHS", he said.
Europol's Wainwright underscored the point Sunday.
In a statement Saturday, Europol's European Cybercrime Center, EC3, said the attack "is at an unprecedented level and will require a complex global investigation to identify the culprits".
Maintain comprehensive data backup systems - make sure that they are easily accessible in the event of an emergency (practice accessing them in a non-emergency)! The exploit was leaked last month as part of a trove of NSA spy tools.
Microsoft took the unusual step of reissuing security patches first made available in March for Windows XP and other older versions of its operating system.
However, it's not connected to the health authority's network.
Pressed further, he said: "I can assure you that the nuclear deterrent is fully protected". "The numbers are going up".
The virus exploits a vulnerability in Microsoft Windows software, first identified by the US National Security Agency.
Ransomware is a program that gets into your computer, either by clicking on the wrong thing or downloading the wrong thing, and then it holds something you need to ransom.
He said the motivation remained unknown but ransomware attacks were normally "criminally minded".
"Ransomware developers and attackers tend to borrow, copy and steal techniques and software from each other", he said.
WannaCry has already caused massive disruption around the globe.
Germany's national railway says that it was among the organizations affected by the global cyberattack but there was no impact on train services.
What is WannaCry - also known as WanaCrypt0r 2.0, WannaCry and WCry? State media reported that digital payment systems at some gas stations were offline, forcing customers to pay cash. Fedex said Friday it was "experiencing interference with some of our Windows-based systems caused by malware".
In Spain, major companies including telecommunications firm Telefonica have been infected.
"Like many organizations our plant was subject to a ransomware attack affecting some of our systems on Friday evening", a spokeswoman confirmed.
The US and Russian Federation were among scores of countries affected by the virus, which also hit a Nissan plant in the UK.
What can you do to protect yourself against ransomware? Here's how to turn automatic updates on.
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