CryptoWall is a nasty threat known as Ransomware. You can't make this stuff up. Cybercriminals have figured out how to lock us out of our own computers, considering that some of us might pay a pretty penny to be able to get back in.
You might ask how they can keep you from getting to your files. Good question. It's kind of like when you were a kid and a much bigger kid took your lunch box and you knew there was no way you could take it back. It's the same thing here, but with no teacher to help.
Cybercriminals at Work