I’m in the middle of moving house and not able to comment at length, but here are some sources for commentary on the Petya ransomware, which, as Bleeping Computer puts it, skips the files and encrypts your hard disk instead. Note that repairing the Master Boot Record doesn’t recover your data.
Darren Pauli for the Register: Ransomware now using disk-level encryption – German firms fleeced by ‘Petya’ nastyware that performs fake CHKDSK . Cites discussion on KernelMode.info forums.
David Bisson for Graham Cluley’s blog: Petya ransomware goes for broke and encrypts hard drive Master File Tables – Chances are you’ll notice you’ve got a problem when the red skull appears during boot-up… He cites Jasen Sumalapao, writing for Trend Micro.