Here is what you need to know about the software behind the global cyber-attack.
How it works:
WannaCry is a form of ransomware that locks up files on your computer and encrypts them in a way that you cannot access them anymore.
It targets Microsoft's widely used Windows operating system.
When a system is infected, a pop-up window appears with instructions on how to pay a ransom amount of $300.
The pop-up also features two countdown clocks; one showing a three-day deadline before the ransom amount doubles to $600; another showing a deadline of when the target will lose its data forever.
Payment is only accepted in bitcoin.
The ransomware's name is WCry, but analysts are also using variants such as WannaCry.
A hacking group called Shadow Brokers released the malware in April claiming to have discovered the flaw from the US' National Security Agency (NSA), according cyber-security providers.