Petya has been in existence since 2016. It differs from typical ransomware as it doesn’t just encrypt files, it also overwrites and encrypts the master boot record (MBR).
In this latest attack, the following ransom note is displayed on infected machines, demanding that $300 in bitcoins be paid to recover files:
Figure. Ransom note displayed on computers infected with the Petya ransomware, demanding $300 in bitcoins