Democratic presidential candidate Barack Obama launched an online viral counteroffensive Tuesday against persistent e-mail chain letters that lie about his religious and political background. But history suggests that the effort might backfire, according to experts in urban myths and folklore.

"The principle is that a very strong denial makes some people think: 'Uh huh, we knew it. If he's taken the trouble to make such a strong denial, there must be some truth to it,'" says Bill Ellis, a professor at Pennsylvania State University who studies contemporary folklore and popular cultural responses to societal events like the 9/11 attacks.

There are various versions of the e-mails, but they generally insinuate that Obama is secretly a Muslim who attended a radical Islamic school in Indonesia. One of the e-mails charges that he's a radical Muslim who refuses to recite the Pledge of Allegiance. Another e-mail claims that he was sworn into the Senate using a copy of the Quran. All of the allegations are false.

According to a list on the urban-legends tracking-and-debunking page Snopes.com, the falsehoods about Obama are the "hottest" urban legends on the internet right now.

Obama's campaign launched a sophisticated counterattack late Tuesday with a webpage called a "Fact Check Action Center," with three paragraphs and a YouTube video testimonial about Obama's background.

The page allows supporters to enter 10 e-mail addresses at a time – or import their Gmail, Yahoo, Hotmail or AOLMail contact lists – into a web form on the site, and with a single click send out talking points that counter the lies in the anti-Obama e-mails.

The page says the campaign won't "hold on to any of the e-mail addresses you share."

The Obama campaign announced the debunking effort with an e-mail barrage from John Kerry of Massachusetts, in which the former presidential candidate urges supporters to "e-mail the truth" to everyone on their address books, to print out the facts about Obama's background and post them at work, and to call local radio stations and talk to neighbors.

"If lies can be spread virally, let's prove to the cynics that the truth can be every bit as persuasive as it is powerful," Kerry wrote in the note.

Kerry's note was titled "Swiftboating" – a reference to Kerry's own presidential campaign in 2004, which was famously sunk by falsities spread by the lobbying group Swift Boat Veterans for the Truth. Many politicos believe that Kerry's decision not to "dignify" the rumors and fight them aggressively contributed to his campaign's defeat in the general election.

But Gary Alan Fine, a professor of social psychology at Northwestern University, who's studied the subject of politics and reputation, suggests that Obama's blanket approach may not be the wisest.

"It underlines the attack," Fine says. "Sometimes defenses against rumors work; sometimes they backfire."

Penn State's Ellis cites an incident from the 1980s that illustrates the problem. The French government was forced to officially denounce a pervasive rumor that lick-and-stick tattoos contained LSD, and that the government wasn't doing anything to protect children against these dangerous products.

When researchers conducted a survey of people and their views of the credibility of the government's claim, they found that those who had already heard the rumors found the government's denial plausible. But those who first heard about the tattoo-LSD rumor through the government denial itself were more suspicious. They thought the strong denials masked an underlying truth.

Fine's advice is for Obama's supporters to be more strategic, and try to feel out friends, colleagues and relatives before sending them the debunking chain letter.

"What you want to do, when you deny the rumor, you only want to deny it to the people who originally heard it," Fine says.