CryptoWall 3 - how to prevent and how to decrypt?

My father's computer is now infected with CryptoWall 3, according to the link below.

http://ift.tt/1DdvSFF

Is there a way to decrypt the files? I will try to recover them but according to the link, the virus safe deletes the copies of the infected files.

What is the best way to prevent these kind of virus to infect our computers? Are there any way to prevent execution of unknown files? I was thinking about only allow execution permission on known files.