"There are tons of ways to monetize any type of traffic you can get," notes Aaron Wall, author of "The SEO Book," a newly published treatise on the art of "search-engine optimization" and other traffic-boosting techniques. "The indirect technique isn't as noticed yet, because so many people are still fighting off the direct stuff," Wall says.

So-called indirect techniques vary. Aside from referrer-log spam -- the general term for what happened to Kestenbaum's site in 2002 -- there's "blog spam" (using bots to post unsolicited HTTP links in the "comment" sections of blog listings), and chat-room spam. Recently, marketers have even resorted to targeting wiki sites such as Wikipedia, taking advantage of their anyone-can-edit policies.

"We've only been noticing it for six months," says Tim Starling, an Australian Wikipedia contributor who has taken a leadership role in the site's attempts to ward off the bot menace. "The bots will go through a site and spam every page. They'll start with the smaller [non-English] language versions, which aren't watched as closely. So it takes longer to pick them up."

In each case, the goal isn't so much to solicit a purchase or confirm receipt -- the tactic of most e-mail spam capaigns -- as to boost visibility. With more than a third of all Internet search queries now running through Google, site marketers have crafted their automated campaigns with an eye to Google's PageRank algorithm, which factors the total number of incoming links to a site as a sign of relevance.

Although Google publishes clearly stated policies forbidding the use of "link farms," -- sites that manipulate link totals as a way to boost (and rent out) page ranks -- the percentage of offenders dropped entirely from Google search listings is microscopically small.

That, says British SEO specialist Phil Craven, leaves plenty of room for other people to push the envelope.

"If a search engine like Google can make link text so important, then people are going to go out of their way to get link text," says Craven. "So-called spamming is perfectly valid, if necessary."

Such words are tempered by Craven's own experience as a target of exotic spam. As manager of the SEO forum Web Workshop, Craven says he recently had to upgrade his site-registration system to ward off bots that had been masquerading as human guests in an effort to deposit links in the open forum and profile sections.

"Basically, the bot would come along and register five names at a time," says Craven. "The names always began with a non-alphanumeric character and ended with a non-alphanumeric character, like a percentage symbol or an exclamation point."

To stop the bot, Craven simply modified the registration process, forcing registrants to confirm their chosen username before getting the usual welcome e-mail. The trick worked only because the bot's author, knowing that most users will run the program in default security mode, didn't bother accounting for such a variation.

"I can do that because I'm a programmer," Craven says. "A lot of forums don't have programmers operating them and they simply wouldn't be able to do it."

Such modifications are similar in their simplicity to the now-common anti-spam technique of spelling out e-mail addresses using "at" and "dotcom." The only thing keeping bot writers from anticipating the trick, Wall says, is the level of effort. Currently, bot writers and copiers find that there are enough newbie operators out there to serve as unwilling page-rank boosters.

"The main thing that's driving specialization is whatever's exploitable and easy," Wall says. "Once it's no longer exploitable and easy, people move on to something else."

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