Recently I've been doing some documentation work for Forefront Online Protection for Exchange (in the cloud) and Forefront Protection 2010 for Exchange Server (on premises). This work has led me to read up more on spam: its source, how it gets around, and so on. This article, Rustock botnet responsible for 39 percent of all spam, caught my attention. It discusses botnets and how much spam they can disseminate.

Botnets are now responsible for sending 95 percent of all spam, up from 84 percent in April, and almost half of that spam comes from a single botnet, Rustock.

Rustock sent 41 percent of the world's botnet spam in August, up from 32 percent in April. This is despite the network actually shrinking in size from 2.5 million to 1.3 million bots over the same period, security company Symantec said on Tuesday. This means Rustock is currently responsible for 39 percent of all the world's spam e-mails.