I have no proof one way or the other if Anthropic or OpenAI have "properly secured corporate networks". Both seem like fast changing places with lots of servers and workers. Seems most likely to me that someone somewhere made a mistake or missed something due to all the change and their network is not 100% secure.

But even if their networks are secure, I think that spies who are willing to coerce people, trick people and go in person to data centers or offices could find a way to get those models and other things.