"If the number of PDF spam e-mail messages have all but disappeared there can only be one reason -- it's not working," said Graham Cluley, senior technology consultant for Sophos. "Spammers wouldn't turn away from PDF spam if it was an effective way to fill their pockets with cash and direct consumers to their websites, dodgy goods or dodgy investment opportunities. The drop in the use of PDFs in spam indicates that the spammers are finding it hard to fool the public into reading their marketing messages distributed in this way."
Experts point to a number of disadvantages for spammers who try and use PDFs in their spam campaigns which may explain its decline.
"PDF spam simply isn't as immediate a way of communicating with your intended audience as an instant glimpse of the marketing message in your e-mail client's preview pane," explained Cluley. "Furthermore, have you tried opening a PDF file? Adobe Acrobat chugs into action, taking a fair while to load before it can show you the contents of the PDF. Consumers pretty quickly learn that it's a waste of time to open every unsolicited PDF they receive, which means the spammer's message doesn't get read, and the cybercriminals don't make any money."
Levels of PDF spam spiked on 7 August 2007, when a single campaign designed to manipulate stock prices accounted for a 30 percent increase in overall junk e-mail levels. Since then, however, PDF spam has shown a sharp decline.
"Of course, it's too early to say that this is the last we will see of PDF spam. There could still be more campaigns to come -- but its dramatic fall may be a sign that we are witnessing its demise," continued Cluley. "Our advice remains the same to all internet users -- it makes sense to ensure that your e-mail inbox is properly defended with a product which can defend against the threats of spam and malware."
