Experts at SophosLabs™, Sophos's global network of virus, spyware and spam analysis centers, have reported a dramatic decrease in the amount of spam email using PDF file attachments to spread their unwanted messages.
According to research done by Sophos, levels of PDF spam have dropped from a high of close to 30% of all spam earlier this month to virtually zero.
PDF spam levels have fallen dramatically.
"If the number of PDF spam email 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."
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 email 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."
PDF spam has been used to try and manipulate share prices.
Levels of PDF spam spiked on 7 August 2007, when a single campaign designed to manipulate stock prices accounted for a 30% 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."
Last month, Sophos published its Security Threat Report July 2007, examining the latest trends in spam, malware and hacking. The report described how spammers were using PDF files to try and escape detection by email gateway filtering products.
Sophos recommends companies protect themselves with a consolidated solution which can control network access and defend against the threats of spam, hackers, spyware and viruses.