Hi Anatoliy,
This kind of stuff sadly happens all the time. I've found passcodes for my products all over the Internet before in the same sort of fashion and there've always been people who try to get something for nothing (buy and return but with no intention of giving up the products)...
It's the way this world works. And it's something you gotta figure into your cost of doing business...
But... look at it this way. For every crook there are 100's of upstanding folks who will do the right thing and those are the people you are interested in in the first place. Focus on them and you'll be Ok.
I doubt that the morons who stole your stuff even had any interest in the content - most of those people do this for the fun of it. And although the information may be reposted somewhere else, I doubt that it really affects your customer base all that much - the people who pay your subscription won't be looking somewhere else to get this information and those who are not inclined to pay you anyway - well, they weren't your customer base in the first place and probably dug out information on the stuff somewhere else.
Don't get me wrong all of this is sad to have to deal with, but there are worse things to worry about from a business perspective...
Keep up the good work and you'll be rewarded with what you deserve. Don't get all riled up over the rubble <g>...