First and foremost, let's clarify exactly what WannaCry is. This malware is a scary type of trojan virus called "ransomware. " As the name suggests, the virus in effect holds the infected computer hostage and demands that the victim pay a ransom in order to regain access to the files on his or her computer.
What exactly does WannaCry do?
RansomWare like WannaCry works by encrypting most or even all of the files on a user's computer. Then, the software demands that a ransom be paid in order to have the files decrypted. In the case of WannaCry specifically, the software demands that the victim pays a ransom of $300 in bitcoins at the time of infection. If the user doesn't pay the ransom without three days, the amount doubles to $600. After seven days without payment, WannaCry will delete all of the encrypted files and all data will be lost.
Source: bgr. com