Bayesian e-mail filters had been studied for years, but with Mr. Graham's paper the idea went mainstream.

Q. What is a Bayesian filter?

A. Many e-mail and spam-filtering programs use Bayesian filters as a tool to identify junk mail and separate it from regular e-mail messages.

SpamAssassin recently added a Bayesian filter, too.

"I think the wide use of Bayesian filters will make spam not profitable, and spammers will just stop using it," he said.

Bayesian filters, a type of statistical filter, are commonly used.

To a rough approximation, Bayesian filters rely on word probabilities.

A Bayesian filter would mark the word "Nigeria" as a probable spam word, but would take into account other important words that usually indicate legitimate e-mail.

In essence, a Bayesian filter works on single words alone, while a Markovian filter works on phrases or entire sentences.

Randomly generated names are more likely to squeeze through so-called Bayesian filters, which keep track of common words used in spam, like Viagra, and weed them out.