It seems that the leak originated from 4chan [1]. Two people in the same thread had access to the weights and verified that their hashes match [2][3] to make sure that the model isn't watermarked. However, the leaker made a mistake of adding the original download script which had his unique download URL to the torrent [4], so Meta can easily find them if they want to. [1]: https://boards.4channel.org/g/thread/9184826…
It would be interesting if there was a WikiLeaks-type of organization that facilitates safely leaking large models from big corporations. Not sure how that would play out for accelerationism and existential risk, but I certainly don't trust the current powers that be.
Modern AI is pretty harmless though, so it doesn't matter yet.