Over the last several years there have been several ransomeware viruses that will encrypt your data in a fashion that will cause you to loose the data or have to pay to get your files back. CryptoLocker, CryptoDefense, CTB Locker, and now CryptoWall. It is now more important than ever to ensure you have backups of all your important personal and business files as you could be infected from any number of sources.
The most common sources seem to be screen saver files (SCR) and flash files (SWF) however these bad guys are constantly evolving their techniques to stay ahaed of the good guys. A recent mapping of the CryptoWall suggests they made half a million US dollars in just a few days after releasing this - including a police department in Tennessee that chose to pay up instead of loosing the files.
The United States accounts for over 50% of all infections suggesting that the Western world is being targeted by these criminals. The remaining countries include Canada, the UK, Australia, and Japan.
Again, if you've slacked off in the past on doing backups, now is the time to become vigilant. Two copies are best, and an online backup can give you access to old versions even if you backup encrypted files.
The FBI is on the hunt and has succeded in catching the CryptoLocker criminals along with their servers and those infected by the older CL can now possibly get their files back. But I wouldn't bet on that. Back up while you can.
UPDATE 12/31/2014: We have found a free utility called Crypto Prevent by FooolishIT. Odd name but a company that we are aware of that has other useful tech tools. They do have a premium paid version as well that automatically updates so may be worth the upgrade - especially for those who forget to back up and have files that are worth protecting. Crypto Prevent has some nuances that you need to read carefully about as it can prevent some programs from installing for example. Use at your own risk, and remember nothing is as certain as backing up.