This isn't the malware where you can shrug your shoulders, clean it off with Malwarebytes and get on with your life.
These trojans encrypt your data and demand payment to unlock it.
If you don't pay the ransom, your data is gone forever. Toast. Irretrievable.

http://www.theregister.co.uk/2014/10/23/cryptowall_malvertising_outbreak/

The bad guys now infiltrate legitimate advertising networks with exploit-loaded scripts, so the old adage of, "lol just don't visit porn sites" or "lol just don't pirate software" is no longer good advice.
The best defense against this stuff is to practice safe computing, install Adblock Plus and keep everything updated.

The second level of defense is to invest in a portable backup drive, update it weekly and keep it disconnected most of the time.
Paying the ransom is way more expensive than investing in a backup drive. Would you pay $50 to get your lost data back? Probably.

You can get a backup drive on Amazon or Newegg for $50 USD. If you can't afford one now, save up and get one. It's worth its weight in gold.
(Black Friday would be a great time to shop for one, btw)

Cloud backups might not be effective because this malware often looks for connected drives (i.e. cloud sync drives) and tries to encrypt them too.
Some cloud services offer versioning which can help, but I wouldn't bet my data safety on this.

Once you get your drive, see my backup guide.