Hi Jason,
Regarding your comment below:
Jason Caldwell wrote:Great question. This is on our @TODO ( PayPal Button Encryption ) list, but it has a low priority at this point in time. If you'd like to make a donation toward the addition of this feature, I'll push it into the next release for you. Otherwise, yes. You can use the PayPal® Generator, just be sure to mirror all of the same values that the s2Member Generator uses.
If you haven't already completed a secure form api I would be interested in donating. I think implementing a secure form is important as looking at it anyone could edit the form on your site and pay as little as they like to access your service and as these are subscriptions each and every payment could be set at the basic minimum.
You would then need to go through the trouble of monitoring all new payments to confirm that the new member did actually pay the correct amount. Paypal pro looks like a good option to prevent this kind of fraud but I am concerned about the amount of compliance required by paypal.
If anyone else is concerned about fraud maybe we all can make a small donation towards the development of the PayPal Button Encryption. We would obviously need to know how much Jason would require to put this at the top of his list and how many people would be interested. Or maybe Jason if not enough takers develop as separate plugging of which I would be your first sale.
regards Pete..