How many ways can you spell V1@gra?

What's most remarkable about the question posed in my title is that I probably don't need to explain it. If you have checked your e-mail anytime in the past few years, you know all about "V.i.a.g.r.a" and "V!A6RA" and "\/lagra".

That's the beginning of a very serious and at the same time amusing article by Brian Hayes in American Scientist Online about spam e-mail, and particularly about its mutations in order to evade the filters that both users and Internet operators have put in place. Spam "is shaped in many ways by our own combat it", he writes. He goes through some maths before concluding that "it seems safe to say there are at least a million ways to spell Viagra" (there are various possible substitutions for each of the five letters V, I, A,G and R; for example, any the 12 characters I, i, 1, l, |, ï, ì, :, Ì, Î, Í or Ï might serve for an I. More: the spelling can also be altered by inserting extraneous characters into the word, such as dashes and asterisks; or some letters could be doubled, as in "Viaggra"; etc)

(Of course, the same logic applies to "C1aL|$" and "Rrol,x Rep,ica" and "pen1s en1argement" and many other such key spam words).

Which spelling ends up in your inbox however doesn't appear to be completely random (although random-spelling generators certainly exist in the spam world). Hayes has mapped the different spellings of "Viagra" in some 10'000 messages he received over time, and the result can be seen by clicking on the image at left (a separate window will pop-up). "The spelling variations might be likened to the spectrum of genetic mutations in a population of bacteria", Hayes writes. "The Viagra variants offer some tentative hints about the working habits of spammers. Often, once a spelling has been incorporated into a message, it is mailed out repeatedly over a period of a few months, then given a rest. The conspicuous vertical correlations within the diagram suggest that mailings with the various spellings are not independent. A plausible inference is that most of the pill-pushing spam comes from a few individuals.