Last November’s shutdown of bot-controller-friendly hosting provider McColo had a surprisingly signficant—and long-lasting—impact on the worldwide spam problem, with some sites reporting as much as a 70 percent drop in inbound spam after McColo’s connectivity was switched off. Despite claims it was a responsible ISP on the forefront of the war against spam, the reality was that McColo played host to a number of systems that served as controllers for vast hordes of bot-infected computers around the world. The controllers at McColo would send commands and data to the infected bots, and the bots would start sending spam and malware out to millions of Internet users. With the shutdown of McColo, spam activity worldwide dropped significantly, and the spread of malware like the Windows-infecting Srizbi and Storm worms largely ceased.
