As image spam continues its decline, the July State of Spam Report highlights more new techniques for delivering spam images, including PDF spam. This is spam that contains no real text in the body of the message (although it may contain word salad), but that has a PDF attachment. When opened, the PDF file is an ad or some other spam message.
The PDF attachments result in messages that are very large in size. We have been monitoring this throughout the past month, but it has really heated up this past week. So far, we have observed over 25 million messages that were categorized as PDF spam.
We have seen a few different variants of this type of spam type thus far. The first one is the newsletter variant, in which a PDF attachment is made to resemble a legitimate newsletter. The second variant is one in which the PDF attachment resembles the more familiar images...