Large-scale WannaCry hack began last Friday
WannaCry is a ransomware program targeting Microsoft's Windows operating system. Ransomware is a kind of cyber-attack where hackers can take control of your computer and keep you from using it or accessing your data until you make a payment to the hackers. If you don't, they can even delete everything.
Ransomware 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.
In the case of WannaCry, the program encrypts your files and demands payment in Bitcoin in order to regain access.
Security experts warn there is no guarantee that access will be granted after payment.
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.
WannaCry is also known as WanaCrypt0r 2.0, WannaCry and WCry.
On Friday, a large-scale cyber-attack was launched, affecting computers in 150 countries, and in less than a day, researchers observed 57,000 infections.
The hackers demanded payments of $300 to $600 which were to be paid using Bitcoin. The British NHS, international shipper FedEx, telecommunications company Telefonica and others were among the targets.
The attack has crippled more than 200,000 computers, and struck banks, hospitals, and government agencies.