Presumably for violating the contract you agree to when you sign up for Pro. As for the GPL being supposed to block this, it doesn't seem to have stopped grsecurity from pulling the same nonsense.
This could work for MIT, BSD and alike. But in case of GPL and other strong copyleft-licensed software - how this is supposed to work? They just can't throw some ToS over it and say "nah, you can't share it", that'd be a violation of GPL (and the only question is if there'd be a developer who would bother to sue for illegally distributing their work).
They shouldn't be able to do that, but that's exactly what grsecurity has been doing to the GPL'd Linux kernel for years, and they've gotten away with it, at least so far.
What is grsecurity doing that violates GPL? I’ve never used it (or even heard of it before now) but just took a quick look at their website, download page, and FAQ. I didn’t see anything that appears to violate GPL.
