[plug] Protecting Online Files

[Chris Watt]

Hi Guys,

I have a client who wants to offer his lessons online as PDF (or
whatever).  He has about 300 of them.

He is very worried about intelectual property and therefore wants to
make it impossible for people to download and redistribute it.

What kind of things have people used successfully for such a venture:?
 There will obviously be a members area, on a PAYG or credit system,
but he wants them to not be able to get hold of the files.

Cheers
~Chris