Pump-and-dump spammers turn to PDFs

Anti-virus researchers at McAfee are reporting a massive wave of "pump-and-dump" stock spam -- with a interesting twist.

Instead of attaching image (.gif) files touting the penny stock, the spammers are now using PDF files with randomly generated subject lines, sender names and blank message bodies.

McAfee's Nick Kelly said the appearance of PDF-based spam makes sense for the spammers because the automation of PDF files is easier than other documents formats.

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