No amount of investment in security software protects companies from social engineering. Eventually, someone needs to have access to core IP and that someone needs to be trusted to do the right thing.

If a lowly engineer can leak this to the public, an intelligence agency hell bent on obtaining source code can certainly have full access to it. I suspect the top dogs (NSA,CIA, Mossad, FSB, China) have full access to source code they deem necessary, with or without the company's consent