This is not hijacking at all. They created a new account, the old one remains blank as the author says. Sure it's morally questionable and leads to having a very bad reputation. But it's not hijacking. GPL code can be forked, mirrored, bundled and distributed. As long as the terms of GPL are obeyed there's nothing technically wrong with what SF is doing. Of course they've completely blown all trust and squandered the…
Alternately one could look into trademark law, perhaps?