Ransomware

Source: SANS security tip
Ransomware is a special type of malware. Once it infected your computer, it encrypts all of your files and demands you pay a ransome if you want your files back. Be suspicious of any emails trying to trick you into opening infected attachments or click on malicious links, common sense is your best defense. In addition. backups are often the only way you can recover from ransomware.
Ransomware