There is a new version of the Cryptowall malware making the rounds. This version is particularly virulent in that it switches between 32 bit and 64 bit system at will. The Cryptowall malware is a ransomeware that holds a user's files hostage by encrypting all files on a user's system and then demanding a payment to decrypt the files. If the user does not pay the ransom in the time given, the ransom doubles. If the user still doesn't pay, the crypto key is eventually discarded. Once the crypto key is discarded it is not possible to decrypt the files and the files are lost. Fortunately this version of Cryptowall doesn't seem to effect Mac users. However, this could change. You can read more bout this here and here.