Ransomware is a type of Malware that prevents you to access the computer. And encrypt your whole system unless a ransom gets paid. It spreading of clicking on an e-mail attachment or visiting a ransom infected website.
Mostly Hackers are trying to deal ransom payment through Bitcoins. After paying by the user victim will get the decryption key to decrypt their computer.
Read Types of Ransomware:
Locky Ransomware: A New Danger Comes Up In The Cyber Era