Sophos has reported a dramatic decrease in the amount of spam emails using PDF file attachments to spread their unwanted messages. According to research compiled by SophosLabs, Sophos’s global network of virus, spyware and spam analysis centres, levels of PDF spam have dropped from a high of close to 30 percent of all spam earlier this month, to virtually zero.
“If PDF spam email messages have all but disappeared, there can only be one reason – they’re 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. This drop indicates that the spammers are finding it hard to fool the public into reading marketing messages distributed in this way.”
Levels of PDF spam spiked on 7 August 2007 when a single campaign, designed to manipulate stock prices of Prime Time Group Inc, accounted for a 30 percent increase in overall junk email 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 make sense to ensure that your email inbox is properly defended with a product which can defend against the threats of spam and malware.”
Sophos 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 victim’s email 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 learn pretty quickly 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.”