Ransomware is a new type of virus/malware which encrypts all of your files. It is generally allowed into your system by clicking on an attachment in an e-mail, but can come from web browsing as well. One prominent version is known as CryptoLocker. This and other variants will find your personal files and lock them down with encryption, and then demand money to get the key to unlock them.
Once the malware encrypts every shared file that it can fine, then the software will notify you with a request for money, in the form of BitCoin. You will have no way to decrypt these files, including files ending in odt, doc, docx, xls, ppt, xlsx, pptx, mdb, accdb, rtf, mdf, dbf, psd, pdd, jpg, srf, sr2, bay, crw, and so on. Pretty much the files that are usually very valuable to you.
Here’s the solution I have found to be best for prevention so far: Malwarebytes Anti Ransomware Click the link and you can review and download the free Beta software from malwarebytes to help prevent this. One caution though, if the system you are using shares folders to other systems, this software will slow that process down to a crawl.