I have, in my view, strong, albeit circumstantial, evidence that a particular user is operating a sock puppet account. It appears not to have been detected by any automated mechanisms–both users are still here.
The individual in question is not interested in collecting lots of rep but rather uses the account to carry out prolonged vindictive down-voting attacks. The down-voting account loses rep over time (due to the down-votes) and when it gets close to falling below 125, it is topped up.
Do moderators want to hear more details (e.g. via a flag)? Or do we just accept that if the automated detection scripts don't pick it up, then there's nothing more to be done.