A new malicious program now makes it even more difficult by completely locking victims out of their computers.

The new Petya ransomware overwrites the master boot record (MBR) of the affected PCs, leaving their operating systems in an unbootable state, researchers from antivirus firm Trend Micro said in a blog post.

Trend Micro researchers say Petya is distributed through spam emails that masquerade as job applications. This suggests that its creators target businesses in particular, with the messages being directed at human resources departments.
This nasty ransomware overwrites your PC's master boot record | PCWorld