Anyone who receives spam – and who doesn't these days? – will likely notice the widespread use of colors, special fonts, pictures, and links to web sites. These features have become so common because most spammers now use HyperText Markup Language (HTML), the Internet code used to develop Web pages, to create visual interest in their messages.
Although spammers do this to make their message more compelling (who can possibly resist if the word “Free” is in red and bold?), they actually have a far more sinister reason. With HTML, spammers can take advantage of a rich toolbox of tricks, encodings, and deceptions in an attempt to fool spam filters.
Compiled by Dr. John Graham-Cumming, a leading anti-spam researcher and member of the ActiveState Anti-Spam Task Force, the ActiveState Field Guide to Spam is a selection of the tricks spammers use to hide their messages from filters, providing examples taken from real-world spam messages. [Privacy Digest]