Thanks, I did not know that. I thought they run something proprietary. I guess now its a closed version it probably is to some extent.
It doesn't matter what they call it—the GNU General Public License (GPL) terms are very simple. The moment you distribute the binary of any GPL-protected code, you are legally required to distribute the corresponding source code. Otherwise, you can be sued for copyright violations, and there have been cases where large companies, like Cisco (IIRC), were forced by law to release the source code to the public.
The problem with Cgminer is that the original cpuminer developers don’t care about the violation of their code. CK himself doesn’t seem to care. Luke-Jr, who forked cpuminer into BFGMiner, doesn’t give a flying fuck. Every major U.S. firm that deals directly with Bitmain doesn’t seem to bother either. I think the latter has every reason to sue Bitmain for the violation—but, well, money talks.
Mind you, for years, people bashed the Chinese (Bitmain, MicroBT, etc.) and the Russians (Vnish) for using the source code without releasing it. But now, you have EU-based companies selling and distributing their own versions of Vnish. You have a Canadian distribution of Vnish. You have U.S. folks making a direct profit off Vnish. Everybody is abusing this shit to make money. 😆