Nice catch, this may be what it was.
Edit: looks like an admin panel was the culprit https://news.ycombinator.com/item?id=23853786
Edit: looks like an admin panel was the culprit https://news.ycombinator.com/item?id=23853786
Tweeting on behalf of another user seems like an unnecessary feature to give admins.
To be fair though, this was not for a social network, and even if you broke into that account there wasn't much you could do beyond paying the user's bills.