tedster - 2:36 am on Jun 10, 2012 (gmt 0)
Not just humans - I'm pretty sure there's a machine learning algorithm involved, and that would make it something like an educated guess.
In this case, there were several years of machine learning, training the algorithm with known seed examples and so on. However, new suspects are then uncovered by an algorithm and humans review that data. Depending on what the humans see, that can trigger a manual action accompanied by a manually triggered WMT message.
At least that's my take, based on watching the evolution of this "campaign".