Project Honeypot just published a report of their experience in processing 1 billion spam messages.  Highlights for the impatient:

• For the past 5 years, spam "bots have grown at a compound annual growth rate of more than 378%. In other words, the number of bots has nearly quadrupled ever year."
• The top 5 countries which host bots are: China (11.4%), Brazil (9.2%), United States (7.5%), Turkey (6.3%), and Germany (6.0%).
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