In mid-summer, you might have noticed a surge in spam in Adobe PDF documents. Proofpoint did. The data security company reports that in late July and early August, PDF spam grew to a dizzying one-quarter of all spam. Considering that 90% of all mail that reaches corporate servers is spam, 25% represents a large number.

Now, though, the PDF spam has plummeted to only 1% of spam. What’s this mean? According to Proofpoint: These sudden crashes are interesting because they indicate a highly centralized command and control structure over global spam that is using tried and true marketing testing techniques to optimize effectiveness. There may be billions of spam messages flying around, but they are generated by a highly structured and centralized organization that is testing and abandoning new techniques based on effectiveness. Spam trend: PDF crashes, MP3 on rise

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