According to data by Shadowserver, the number of botnet-controlled machines has tripled in the last month. Specifically the jump seemed to start on March 8th or so and has kept going ever since.  For the most part, they haven't tracked a significant increase in the number of botnets (only about a 20% jump), just the number of machines. The biggest C&C nets are near New York, Southern California, and near Germany. The biggest concentrations of botnet infected machines are in China, Brazil, and Argentina.

So it appears botnet controllers are getting better at increasing the size of their herds.

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John Bambenek / bambenek /at/ gmail.com
University of Illinois at Urbana-Champaign