What is Ransomware? Ransomware is a virus that infects your machine and renders it useless until you pay the ransom amount.
In most cases it encrypts all files on your computer rendering them inaccessible as well as all connected devices, this includes other computers on your network and backup drives that are attached - this includes cloud drives like Dropbox!
If you are thinking you're safe on a Mac - think again! Mac computers are also a target of these viruses.