Dot Matrix Spam

Just when I thought I'd seen every imaginable effort by spammers to circumvent antispam programs, they try something new. The latest stunt is a bit of a throwback to the 1980's.

Almost all printers use dots to make up characters on a page. New printers use thousands of dots per inch. Some early printers used a "daisy wheel" - to create characters the same way a typewriter does. Most users used "dot-matrix" printers due to their low cost and ability to print graphics.

The least expensive printers only used 9 pins to create their images and text. The result was quite legible but fairly blocky. Recently spammers have picked up on the effect to encode their message in spam.

#     #  #    ##     ####   #####     ## 
#     #  #   #  #   #    #  #    #   #  #
#     #  #  #    #  #       #    #  #    #
 #   #   #  ######  #  ###  #####   ######
  # #    #  #    #  #    #  #   #   #    #
   #     #  #    #   ####   #    #  #    #

Sometimes it's possible to detect this type of thing simply by recognizing the unusual repetition and spacing of characters. One of the virtues of fuzzy logic is that this type of data can be factored into the scoring system of the spam filter program without needing to be entirely sure if its indicative of unwanted email.

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