Came to ask the same thing. If you're distributing a modified version of a GPL project, and not providing the source, you're committing license violation.

Closed source is bad enough by itself for a lot of reasons. Especially in cryptocurrencies which are open community efforts. It's even worse if you're admitting you're leeching off community code.

I'm assuming you don't feel like releasing the source because of the donation/fee percentage. Frankly, I don't have a good answer for that -- I've released some opensource code myself, and I sometimes feel I've been cheated by some Chinese knockoff projects that use my code without crediting me. But I guess imitation is the sincerest form of flattery Meaning that there are ways to make an honest living with opensource code. For starters, respect the licenses and maybe people will also respect your coding skills.