Petya represents is new  twist on crypto. It was found recently targeting companies in a spam campaign. The emails contained a link to a Dropbox file that if clicked loads a dropper that installs Petya. Dropbox has since removed the link and several others that were associated that also contained the same malware.

If the archive is downloaded and executed, the ransomware is installed. Petya does not encrypt the file data itself, which would take a long time for an entire hard drive, but by encrypting the MFT the OS will no longer know where the files are located on disk. Then the  malicious program will  trigger a critical Windows error that will cause the computer to reboot — a condition known as a Blue Screen of Death (BSOD).