Re: Is there single key ?
QUOTE: "The idea that a decryptor can hold 'all the keys' is too fancyful. Must be more to the story."
No, its not fancy, it is technically viable and has been done in the past already (I believe I read it somewhere).
Supposing 4000 systems were infected and each key has 512 bytes in size, it will add 200Kb to the final .EXE size to hold all the keys, plus the extra algorithm part to test each key for 1 file, succeeding, use that key in the rest of the encrypted files.