Could you not put it on your site without a link so that people can’t find it until you send them the link?
Won't work...........the current firmware are on the web server but have been protected through the "ordering" system for quite a long time. However, lately I realized that someone literally copy it and host it on their server, they didn't even rename my zip file!!!! That's why I have been losing a lot of sales because they are literally make a profit out of my efforts. (you won't believe how much time and effort we spend to get the new firmwares........it is ridiculous. Hence, the new model.....100% build by us.) It is not about bandwidth stealing nor hiding the location of the actual file......
As added protection you could also put the file in a password protected encrypted zip or rar archive.
I have thought of it, but it won't work because once it is the file is extracted, you can always re-zip it. Plus, it will only cause troubles to the customers if they don't know how to extract it.
You could then email all your customers the link and password assuming you have a mailing list for them all.
The problem is I don't know how they get hold of my firmware. They must have either pretend to be my customer to get it or get it via one of my customers. Or one of my customers provide uploading it somewhere after they have downloaded it.
I have been thinking but seriously, there isn't much I can do about it............