In response to the news that a new spam campaign leveraging Intuit brand name has been spotted delivering messages with CryptoWall malware attached claiming to be the copy of a remittance file, Mark James, security expert at ESET says:
“Cryptowall is another of the ransomware programs that can be very easily protected against both in stopping the infection and resolving the problem. Once you are infected (encrypted), it spreads via emails (zip files) usually telling you about some money your owed or some important government information that needs correcting or verifying.
In order to stop infection from this malware, computer users must have a good up-to-date Antivirus installed on their PC. If an email comes in and there is free money involved there's a very high chance its fake, when was the last time someone banged on your front door to hand out ten pound notes?! If your still unsure if it's real or not CALL or contact the company and ask the question, if there's no contact info then DELETE the email, DO NOT open any attachments, DO NOT run any files in that email. If you really have won some money a few more days or another 30 minutes won't make that much difference to your life.
If you do manage to get yourself infected and all your files are encrypted then you only have ONE option, you have to restore from backup. With the massive amount of backup solutions (external hard drives, flash drives, cloud backup) available these days it really is very inexpensive to do a backup at the very least weekly (preferably daily). The encrypted data is using RSA encryption which means it's virtually impossible to decrypt without the private key, so that avenue is out of the question. Should you pay the ransom? No, that would mean you are funding criminals plain and simple, the average fee is £500 to start, a 3TB external drive from a reputable well known website is around £80.”