It doesn't DELETE anything.

It encrypts personal files (leaves the system alone) like documents, pictures, videos, mail, etc. And it does so with impenetrable encryption. You then have a short period of time in which to pay the ransom, which is pretty steep ($300-$400). If you DON'T do so, then the criminals delete the encryption key from the server, which means your files can never be recovered.

They aren't deleted, they just sit there on your hard drive taking up useless space, like most of Congress.

It's too bad they can't target these ***$*%)$*(%&)#$(*& people with some drone strikes.