As spam filters get increasingly effective, spammers are changing their tactics to foil anti-spam software and get through to your inbox. Recently, this has involved a shift from the use of text-based spam to the use of embedded images and PDF file attachments as the preffered delivery method for their spammy intrusions.
Image Spam
The prevalence of this form of spam increased in 2006, primarily as a means for advertising penny stocks. It involved the use of a picture or graphic embedded in the body of the junk email. The junk email’s message is displayed as an image.
Because most anti-spam filters are text-based, image spam was relatively successful. This led to its use in advertising everything from sexual enhancement to fake pharmaceuticals.
One serious effect of image spam has had is to further clog up Internet bandwidth, and drive up costs to businesses. This is because the average size of each junk email almost doubled. In fact, this increased size and the sheer volume of image spam forced many businesses to block all emails that contained embedded or attached images.
By early 2007, image spam reached an all-time high, accounting for almost two-thirds of all junk email. However, as spam filter technology has adapted to detect image spam, its use has since declined to less than 15% of all junk email. Instead, spammers are turning to PDF spam
