LLMs really are stunningly good at finding vulnerabilities in code, which is why, with closed-source code, you can and probably will use them to make your code as secure as possible.
But you won't keep the doors open for others to use them against it.
So it is, unfortunately, understandable in a way...
LLM like humans can find vulnerabilities in black boxes. We already established 30 years ago that open source is usually more secure than closed source and that security by obscurity doesn't work.
You don't need the source, the LLM has the source, it is called the binary.
I'm not a security expert but can't close source applications be vulnerable and exploited too? I feel like using close source as a defense is just giving you a false sense of security.