Campbell and his team were able to get more "Google juice" out of these sites by linking them together and persuading other bloggers to link to them. They also strategically placed phrases on the doctor's website, and distributed electronic press releases about his practice and products that included those phrases.

The order in which results appear in a Google search depends on an algorithm—a mathematical formula—that weights various websites differently as well as the positioning of keywords or phrases on those sites.

Google favors content with lots of links, particularly from sites it deems credible, including CNN, The New York Times, and, yes, Portfolio.com. The doctor was lucky that he had a link from an affiliate station of a TV network.

A study by iProspect and JupiterResearch indicates that fewer than 30 percent of people go beyond the first page of search results, and less than 8 percent make it to page three. Reputation-management experts say they concentrate on Google because it's the most popular search engine and others often mirror its results.

"When you think about how Google results impact whether you get a client, attract investors, or even get a date, you understand how huge the demand is for this type of service," says Chris Martin, founder of ReputationHawk, a reputation-management company in Baton Rouge, Louisiana.

The potential for abuse has grown as the internet has become more interactive with blogs and sites like YouTube, Facebook, and MySpace. "Anyone with a computer can disseminate lies around the world in seconds," says David Pollack, a Miami lawyer who last year won an $11.3 million verdict in an internet libel case.

Pollack's client in that case, an education consultant, was vilified by someone she had once advised. Following the verdict, Pollack says he has received hundreds of calls from people who feel they have been similarly wronged.

Suing to defend your online reputation is a difficult and expensive strategy, since most calumny is posted anonymously. Moreover, the Communications Decency Act of 1996 immunizes webmasters, Web hosts and internet service providers from liability if a third party posts something malicious on their platforms. (A judge can compel them to reveal the identity of an author if harm is established; that person can be held liable.)

"It's a long and drawn-out process, but it is possible to unmask anonymous posters," says Karl Kronenberger of Kronenberger Burgoyne, an internet law firm in San Francisco. "Even the most technologically savvy person leaves a digital footprint."

Kronenberger's clients have included a Cayman Islands medical school and a Florida relocation service. Competitors had anonymously disparaged them on consumer websites. Once exposed, the competitors were induced to retract their rants and pay damages.

Even if the person responsible for posting defamatory information is, say, an unemployed crank living in his parents' basement without financial resources (as often is the case), lawyers say that homeowners' insurance policies may cover the damages.