It's called ransomware. Fabrice Bellard (http://fabrice.bellard.free.fr http://fabrice.bellard.free.fr), who is not your average hacker, tried this model with

It's called ransomware. Fabrice Bellard (http://fabrice.bellard.free.fr http://fabrice.bellard.free.fr), who is not your average hacker, tried this model with kqemu and as far as I know, despite the great quality of his work, it didn't work (he finally decided to release the thing under the GPL). Stephen King tried a similar system for a novel and it didn't work either (he quit writing it). John Carmack has a model that works: initially release the thing under a proprietary license, make money with it and then release it as open source software.