Also - Vaccine, not Killswitch, Found for Petya (NotPetya) Ransomware Outbreak
To vaccinate your computer so that you are unable to get infected with the current strain of NotPetya/Petya/Petna (yeah, this naming is annoying), simply create a file called perfc in the C:\Windows folder and make it read only. For those who want a quick and easy way to perform this task, Lawrence Abrams has created a batch file that performs this step for you.
Please note that he batch file will also create two addition vaccination files called perfc.dat and perfc.dll. While my tests did not indicate that these additional files are needed, I added them for thoroughness based on the replies to this tweet.
This batch file can be found at: https://download.bleepingcomputer.com/bats/nopetyavac.batHopefully this helps somebody.