I had a similar experience. I founded a company 3 years ago where we open source the majority of what we do. We entered into a discussion with a well funded (>$40M) "startup" about how they could use our service as a whitelabeled SaaS offering to their customers.
After a few promising exchanges including a Skype call with their Founder and VP of Engineering they stopped returning all of my attempts to see what the next steps should be. Turns out the reason was because they forked a private repository of the work we did - web, iOS and Android.
We found out they're using our code because they didn't even bother taking out our Crashalytics code and we started to get a bunch of pings. To this day their iOS app still uses our "yellow" color for toggle buttons.
https://www.dropbox.com/s/dcpbbnbltm2bmq6/Photo%20Mar%2026%2...
They didn't violate any terms of our license (MIT) but I lost some faith in humanity because of what they did :).
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My company is Trovebox - code @ https://github.com/photo