Computer viruses that threaten to delete your files unless you pay a ransom are known as ransomware.

Security experts have warned that ransomware is the fastest growing form of computer virus.

Like other computer viruses, it usually finds its way onto a device by exploiting a security hole in vulnerable software or by tricking somebody into installing it.

Article Source: >> http://www.bbc.co.uk/news/av/technology-35091536/what-is-ransomware