A short introduction to the Cryptolocker Virus

This virus is not quite like your average virus, its known as a ransom Trojan which means it will disguise itself as a something such as a .pdf file etc and execute a program that shows an error message saying “your files have been encrypted”. Now back in 2013 when this virus was detected it was just a scam to get victims to pay a ransom to “keep their files” when in reality it would never truly encrypt them just disable access. However now there have been numerous cases of people having their files actually encrypted and haven’t been able to get them back. Either way whatever you do IT IS RECOMMENDED THAT YOU DO NOT PAY ANY RANSOM. This is simply because you are never guaranteed your data back, there have been some cases where people have paid this ransom and still have no access to their data, plus if you pay the ransom then they will continue to do this and therefore endanger more and more PCs.

Can this be prevented?

Yes however when your PC has already been infected with this virus there is only some chance you can get your data back 

Read more.......
http://dlsr.co.uk/cryptolocker/