Well on the plus side. Were lucky as we just so far have one such troll. For a time we locked things down as he was very aggressive after being discovered to have 14 sleeper accounts in place.
Our core members in tye community have become an excellent resource in keeping his efforts wasted. We figure eventually he will tire or find a new shiny thing to grab his attention.
We have installed the Fingerprint plugin that also helps to a small degree as well.