A little OT... This presentation from this year's Black Hat Briefings is really quite interesting --
http://www.blackhat.com/presentations/bh-usa-04/bh-us-04-kret.pdf It really does look like there may be some use of spam, specifically hashbusters and "chaff" headers, as a covert channel. However, the presentation doesn't seem to note that there *is* use of it for some covert data -- namely the encoded email address of the recipient, for list-washing.... --j.
