Update on Petya Attack
As noted by our on-site expert, krakatoa, the current vaccine for Petya involves creating a file called perfc in the C://Windows folder and making it read only. No kill-switch has been discovered, only a local vaccine.
If you see the reboot notification below, your device has been infected. Turn off your device to prevent future encryption. Petya begins encrypting the device an hour after the initial infection.
**Update: Petya begins encrypting your the first 1MB of your files prior to the reboot. See new post for the updated information. **