See the Youtube video, noting the comments between timemarks 07:00 to 0:00.
Adam Kujawa, Malware Intelligence Analyst, Malwarebytes
Virus Advisory: CryptoLocker - How to Protect Yourself
LinuxTechShow
http://www.youtube.com/watch?v=Zcj9RKO3e38
Some of the suggestions of using group policy to disable some execution prevention isn’t a bad idea, but it’s impractical for some enterprises that use a wide variety of applications. :-(