Hi, first of all, thank you all for identifying the scumbag in question, and working diligently to frustrate his efforts.
I see from posts #23 and #24 that SB does offer two-factor authentication, which is a great security feature. I just opted into it myself. 2FA is designed to solve the class of problems Pete described in post #51, and would have kept those accounts safe, even if their passwords were leaked.
@The Chairman have you considered making 2FA mandatory for all SB users? Or if that is problematic in some way, perhaps just the admin/mod team, which were targeted for these reputation-dependent attacks? I don't know whether XenForo supports making 2FA mandatory, but the increased security might be worth the inconvenience tradeoff to users. Just a thought, thanks again for all you do around here.
Edit to add: or a third possibility, make 2FA mandatory for accounts posts the classified section. Again, not sure if XenForo supports this, but it might be the least restrictive way to gain the security improvements where it would be most useful.