http://www.nytimes.com/2006/05/21/business/yourmoney/21spam.html
Matt Sergeant (of MessageLabs, and one of the early SpamAssassin committers too!) is interviewed about spam, with a bit of relevance regarding image checksumming (which we've been talking about recently): The spammers were trying to circumvent the world's junk-mail filters by embedding their messages -- whether peddling something called China Digital Media for $1.71 a share, or a "Hot Pick!" company called GroFeed for just 10 cents -- into images. It worked, but only briefly. Antispam developers at MessageLabs, one of several companies that essentially reroute their clients' e-mail traffic through proprietary spam-scrubbing servers before delivering it, quickly developed a "checksum," or fingerprint, for the images, and created a filter to block them. [...] Shortly after MessageLabs created a filter to catch the stock spams, the images they contained changed again. They were now arriving with what looked to the naked eye like a gray border. Zooming in, however, the MessageLabs team discovered that the border was made up of thousands of randomly ordered dots. Indeed, every message in that particular spam campaign was generated with a new image of the border -- each with its own random array of dots. [...] "We actually developed some technology to detect borders in images and figure out the entropy -- that is, to figure out if the border was random," Mr. Sergeant said. "So that was fine." Of course, shortly afterward, "they decided to stop using the borders," he added. From there, the senders began placing a small number of barely perceptible and, again, randomly placed dots -- a pink one here, a blue one there, a green one near the bottom -- throughout the images. Then they shifted to multiple images, with words spelled partially in plain text and partially as images, so that the content, when viewed on a common e-mail reader like Outlook or AOL, would look like an ordinary message. Aside from that techie stuff, it's a good interview too ;) --j.
