Hi Criag,
congratulations for the excellant idea. Well, if you want to protect your work from those not-worthy people, and if you are ready for some more time and effort then here is another way round if you are interested.

1. The file is available only for registered people and
2. They post a request for the file and (after verifying their authenticity or what ever) you grant them access to the file.

I know this is not totally fool-proof but helps to a large extent but at the expence of some more time of yours.

Cheers
Harsha.