The current  Petya 'ransomware' is emerging as an information warfare malware. It  seems primarily aimed at destroying data  on Windows systems rather than ransoming. There appears no way paying the ransom will result in your data being decrypted. Petya  can spread throughout organisations and servers, including backups and both encrypts the data and does irreversable damage to hard drives.  Information warfare primarily involves one party degrading the assets of another party. The current Petya infection appears to follow this path rather than that of criminal intent.
A cure for Petya infection is potentially possible for those quick to act.

If a computergets infected, this is first indicated by a request to reboot the computer. If the computer is immediately turned off, the harddrive can either be removed and the files recovered on an uninfected machine OR  the computer can be booted with a  live OS  and the data removed. In both cases, the hard drive will need to be then cleaned and the software and data reinstalled

It appears that effective protection includes ensuring security patches are up to date and using anti-malware software  - several anti-malware vendors claim to provide protection against the current Petya malware.