Cryptolocker is the latest in the ransom viruses, but is the nastiest and most effective. I have done everything to safeguard my computers.
As Tom said, the best thing to do is have good backups. I have heard that they will send you key which can be up to $2,000 depending on how long you take to pay it. It doesn't make sense for them to not give you the key as if that got around no one would pay it.
The only anti-virus I know of is MBAM, which can work side by side with your AV. It detects in a variety of different ways, one of which is blocking websites which are known to send it.
You have to have backups of all your computers everyday. No admin accounts on your staff's computers and user User Account Settings. Update the MBAM definitions every hour and keep your Windows updates current.
It is also best to use the SBE/Corporate edition, which needs licenses for MBAM. I run a scan once weekly for both A/V Malware detection.
