Many experts believe that solving the spam problem will require a combination of approaches. But laws take forever to pass and amend. Technological fixes like sender authentication and electronic stamps would also take time to carry out, but filtering is already here - and it is reducing the spammers' messages to feeble signals swamped by a roar of alphanumeric noise.

The turning point came in August 2002 when a computer scientist, Paul Graham, issued a manifesto called "A Plan for Spam," describing how to filter e-mail using a statistical method discovered in the 18th century by the English theologian and mathematician Thomas Bayes. Bayesian e-mail filters had been studied for years, but with Mr. Graham's paper the idea went mainstream.

Presented with thousands of examples of good and bad e-mail, a Bayesian filter compiles a list ranking each word according to how likely it is to appear in junk e-mail. Rising to the top of the roster are high scorers like Valium, Xanax, mortgage, porn and Viagra. Settling toward the bottom are words like deciduous, cashmere and intensify. Hovering in the middle are the vast number of neutral words that can swing either way.

When a new piece of e-mail arrives, the filtering program counts up the words and computes an overall ranking. If the number exceeds a certain threshold, the message is rejected as spam.

A message from a friend saying that she is so worried about refinancing her mortgage that she took a Valium will pique the filter's interest. But most of the text will probably consist of words with neutral or very low rankings, dragging down the score and allowing the e-mail to go through.

If a spam promising "l0w m0rtg@ge rates" slips by, the filter is informed by the user that it has made an error. The mutation is then moved higher on the list, as well as future mutations of the mutation, until the spammer is reduced to sending gobbledygook. A recent e-mail message making the rounds promised "Leacatharsisrn to make a fortcongestiveune on eBay!" (A Web link inside led to a site with information on a money-making auction scheme.)

Increasingly the subject lines convey no meaning at all: "begonia breadfruit extempore defocus purveyor." For the spammer, the hope, slim as it seems, is that a few curious souls will open and read the e-mail, which begins, "I finally was able to lsoe the wieght" and goes on to offer a product "Guanarteed to work or your menoy back!" Read out loud, the message sounds a little like HAL the computer in "2001: A Space Odyssey" sinking into aphasia as its synapses are severed one by one.

In what may be their final death throes, some spammers have begun sending messages consisting of a single image or a one-line sales pitch - "picospams" - with a link to a Web site. Often appended at the end, in an attempt to flummox the filters, is a scrap of Dadaist poetry - "feverish squirt feat transconductance terrify broken trite fascist axis stultify floc bookshelves. " Sometimes this "word salad," as it has come to be called, is rendered in invisible ink - white letters on a white background - or hidden inside an embedded formatting command.

No matter. The filters learn to adapt. If the spammers want to stay in business, ultimately they must convey at least a hint of meaning. After all, you cannot send a completely random message - or one that is blank - and expect many people to click the link.

[via Follow Me Here]