It appears that PDF spam has had its 15 minutes of fame. Having reached its peak volume on August 7 at nearly 30% of all spam messages sent, PDF spam today is hardly registering on email security vendors’ spamometers.The unwanted emails with PDF files attached — usually pushing the recipient to purchase a penny stock that the spammer then dumps once the trading price goes up — comprise less than 1% of spam today, according to security vendor Sophos.PDF spam began hitting high volume levels in early summer, the highest of which occurred on August 7 when a pump-and-dump stock scam exploded across the internet, touting a company called Prime Time Group.
http://computerworld.co.nz/news.nsf/scrt/E77968CC14DF2706CC257347000EC4FBAlso see:

Sophos reports on the rise and fall of PDF spam Is PDF spam simply not working for the spammers? [news release]

Experts at SophosLabs 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.”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.”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.
http://sophos.com/pressoffice/news/articles/2007/08/pdf-spam.htmlRead more on the SophosLabs blog about the rise and fall of PDF spam:
http://sophos.com/security/blog/2007/08/543.html