McColo, according to Washington Post investigative reporting, was involved in as much as 75 percent of the world's spam traffic flow.
That flow dropped from more than 30 spams per second to barely 11 per second. Take a look at this graph to get a sense of the size of the drop-off.
McColo traffic also, it almost seems unecessary to say, included malware, child pornography and other problematic (to put it too mildly) content.
The hero here is Brian Krebs of the Post, whose dogged pursuit of documentation of McColo's centrality to the spam flood gave McColo's Internet providers the stats they needed to pull the plug.
No one expects the drop-off to be permanent.
Indeed, volumes are already beginning to creep back up.
But there are lessons here as well. Krebs's example -- track the traffic to its source and make that data available to the source's providers -- is a model of both excellent reporting and effective reporting.
And a model, too, it seems to me for pursuing and shutting down the next high-volume spam host, who should be appearing real soon now, alas.