An unusual kind of ransomware cyber-attack has taken the world by storm, causing calamities in various parts of the world.
The virus exploits a vulnerability in Microsoft Windows software, first identified by the US National Security Agency.
In Britain, whose health service was among the first high-profile targets of the attack Friday, some hospitals and doctors' offices were still struggling to recover.
This follows the massive cyberattack that hit 99 countries across the world, as cybersecurity researchers said they detected 36,000 instances of the ransomware called "WannaCry virus" and variants of the name. It was benign because it contained a flaw that prevented it from taking over computers and demanding ransom to unlock files but other more malicious ones will likely pop up.
NHS Digital says it is working closely with the National Cyber Security Centre, the Department of Health and NHS England to support affected organisations and to recommend appropriate mitigations.
Can you protect yourself against a ransomware attack? It spreads from computer to computer as it finds exposed targets.
The WannaCry ransomware affects the computer systems and asks the user to pay a ransom of $300 in Bitcoins to restore access to the systems or its data. Microsoft did put out a patch two months ago for more recent systems, but not all users may have downloaded it. Microsoft swiftly announced that it had already issued software "patches" to fix those holes, but many users haven't yet installed updates or still use older versions of Windows. And that's for a simple reason: Individuals and organizations alike are fundamentally awful about keeping their computers up-to-date with security fixes.
WannaCry has so far infected tens of thousands of computers in at least 74 countries, according to cybersecurity companies who are observing its spread across the globe. It said the majority of the attacks targeted Russia, Ukraine and Taiwan.
Security experts said the attack appeared to be caused by a self-replicating piece of software that enters companies and organizations when employees click on email attachments, then spreads quickly internally from computer to computer when employees share documents.
In Brazil, the social security system had to disconnect its computers and cancel public access.
James Clapper told ABC's "This Week" on Sunday that he expects similar attacks to become a growing problem in the future.
Patients arriving at Dharmais Cancer Hospital had to wait several hours while staff worked with paper records.
The Shadow Brokers released Eternal Blue as part of a trove of hacking tools that they said belonged to the US spy agency.
Russia's central bank said Saturday it had seen no incidents "compromising the data resources of bank institutions", state news agency Tass reported.
Spain, meanwhile, took steps to protect critical infrastructure in response to the attack.
"This attack provides yet another example of why the stockpiling of vulnerabilities by governments is such a problem", he said.
Ransomware attacks are on the rise around the world. Lieu said it is "deeply disturbing" the NSA likely wrote the original malware used to ransom computers. They were forced to reschedule patients, and people were warned to stay away from emergency rooms if possible.
Over the weekend, the ransomware has hit systems in more than 150 countries, including Russian Federation and the United Kingdom, in one of the most widespread cyber attacks in history.
"Looking at the trends, it was going to happen", he said.
Whatever the motive, the huge scale of the attack shows that cybersecurity can have unsafe geopolitical consequences. Parra reported from Madrid.
Lawless reported from London.