Many would argue that filing a complaint with the FTC is futile. But, I have seen first hand that this avenue can bring results.
And don't take this sitting down. Let them know your intentions on their webmaster contact page,
http://www.enigmasoftwaregroup.com/contact.php
To our benefit, their product is Non-adult related, so the authorities tend to take the complaints much more seriously. I can't speak for everyone else here, but I assume that everyone sent them traffic through legitimate means...which makes Enigma Software's failure to pay both fraudelent and illegal.