Ransomware, such as Cryptolocker, is very real. I have had 5 clients in the past two months who had become infected, and there is nothing that I, or anyone, else can do to retrieve their files. All their photos, documents, spreadsheets, music and more have all been rendered useless, forever.
Please backup your files. This is the only real way to be completely safe. I strongly suggest and online service like Carbonite.com or Mozy.com. If you must use an external hard drive, do not leave it plugged in to your PC, as attached external drives will also be encrypted.
Do it this week.