Ransomware is a sophisticated piece of malware that blocks the victim’s access to his/her files or computers. The malware does this by encrypting or making all the files on the victims’ computers unreadable and then ask for money to decrypt or make the files readable again. Ransomware may also block access to the victims’ computers by locking them out, therefore, preventing them from working on their computers. This is why this type of malware is called a Ransomware because it holds your PC or files for "ransom".
Cyber criminals or hackers flood mailboxes with spam thus pushing out fake documents that deliver ransomware. This attack relies on users opening attached malicious document that will appear legitimate. Therefore, it is important that recipients of unexpected email messages never open the attachments in them.
I have seen people lost years of cherished family photos and important documents because of Ransomware. So, it is important that you get paranoid when opening an attachment that came in an unexpected email message. This is because email attachment is one of the oldest and easiest ways of infecting a computer with ransomware, viruses, spyware or other malware.