Joe Chongq sent me a fascinating spam that is the first I've seen that's using a PDF file to send its information. I've long predicted that we'll see a wave of complex formats used for spam as broadband penetration increases and sending large spams becomes possible.
This particular spam has a couple of interesting attributes:
1. The PDF file itself is a really nicely formatted report about a particular stock that's being pumped'n'dumped.
2. The file name of the PDF was chosen to entice the user further by using their first name. In this case it was called joe_report.pdf.
3. The PDF is compressed using the standard PDF 'Flate' algorithm and totals 84,398 bytes. That's fairly large, but we've certainly seen image spams that were larger. Use of compression here means that a spam filter that's not aware of PDF formats would be unable to read the message content.
Here's what the actual PDF looks like (click for a larger view):