Dec. 12, 2008 -- A man standing on a street corner with a sign reading "the lizard people rule you all," or, "my neighbors are spying on me for the government" isn't likely to get many supporters.

But give that man a Web site template, or let him produce some slick videos on YouTube and, lo and behold, he may have thousands of people across the world supporting him.

Such is the story of several extraordinarily popular conspiracy theorists and theories online today.

Take the victims of gang stalking -- a subculture of people who think their friends and neighbors are all secret government spies ready to turn them over to the authorities. The movement has recently spawned gang stalking support groups, forums and advice Web sites.

Or take the former journalist and BBC sports announcer, David Icke, for example.

Icke was laughed out of the public eye in the early '90s when he started wearing only turquoise and explaining that voices had sent him on an important mission to save the earth.

Decades later, Icke has written books, has fans in 47 countries and can gather a crowd of 2,500 people in a city simply by posting a date for a lecture on his Web site.

The cornerstone of Icke's theories is that a malicious race of lizard people -- the "shadowy elite" -- rules the world and all its political leaders primarily by controlling the media and orchestrating fear-mongering catastrophes, such as Sept. 11. Icke said he already has speeches lined up for 2009 in Los Angeles, Mexico, Croatia, New Zealand and Australia.

"I knew about the mainstream media, and that the mainstream media has a stunning level of myopia so that only that which is in the mainstream will be presented," said Icke. "What the Internet has done [is that it] has allowed information to flow outside of the myopia. ... The Internet has been absolutely essential."

The Internet has always been a forum for fringe ideas, but success like Icke's, and subcultures built on paranoid theories like gang stalkers, points to an understudied corner in psychiatry: Who are the people who believe such theories in the quiet of their homes, and what does such behavior mean for a person teetering on the edge of mental illness?

"It's not an area that has been studied very well," said Angus MacDonald, a spokesperson for the mental health charity NARSAD, and an associate professor of psychology at the University of Minnesota in Minneapolis.

Does Conspiracy Always Equal Delusion?

MacDonald cautioned that not everyone who believes in a conspiracy plot is mentally ill. They just may be suggestible or just suspicious of authority.

For the healthy in mind, MacDonald said, "it's a wild card about whether this is going to improve people's state or not. It may turn out that the value of the community is greater than the destructive nature of the narratives that are spun out of them.

"But on the same point, this is a domain that didn't need more wild cards," he added.

Whether or not conspiracy theories harm people who are susceptible to mental illness is a matter of debate among psychiatrists.

"Most people with major mental illness don't believe in conspiracy theories," said Dr. Ken Duckworth, medical director of the National Alliance of Mental Illness.

Duckworth likes to imagine a Venn diagram with one circle representing people with paranoid psychosis and another circle representing people who believe conspiracy theories.

"They do overlap, but I can't tell you how big the overlap is," he said. "And, lizard people? Many people who are hearing voices would think that's crazy."

Duckworth argued that most mentally ill people create conspiracy theories that are self-centric, such as, "the mailman is after me," not inclusive such as, "the postal workers are all out to get us by 2015."

But others who treat schizophrenics and people with paranoia think there is a risk in circulating online conspiracies.

"Paranoid is wide category -- it's another way of being separate with reality -- but in our culture, we've made it synonymous with persecutory delusions," said MacDonald.

The Making of a Conspiracy: Delusion or Not?

According to MacDonald, most delusions begin with general, unexplained feelings of discontent that are caused by a problem with the brain. It's only when someone tries to search for an explanation for their feelings that a delusion forms.

"Then over time, the delusions become crystallized -- meaning they take on particular narratives, story lines and people's motives begin to be fleshed out," said MacDonald. "When one thing isn't explained, it's never abandoned. The plot just thickens ... and you credit your persecutor with a tremendous amount of power."

MacDonald said it can make it difficult to do talk therapy when delusional people feed their story from outside sources or find evidence with other conspiracy plots.

"You're sitting across from your therapist and they say, 'Well why would they do all of this?' And you've got the answers because you've studied online," he said.

Icke said that sort of danger is not his responsibility.

"You can't stop information because it might be misused by people," he said.

"What people think of my information is none of my business; it's their business," he added. "I'm not saying, 'This is how it is, you must believe it.' I'm saying, 'This is another way to look at the world. What do you think?'"

Icke said he has run into psychiatrists analyzing why people believe his theories in television interviews.

To them, Icke says, "Check it out. Check it out. Then [decide]: Do the facts stand up? Don't go into this psychological babble after you first dismiss the information by reflex action."

Icke believes his popularity on the Internet is a testament to the validity of his ideas, and that people feel that his predictions have come to pass.

"What you do as you continue to research and you continue to travel is you hone it down," he said. "I've never come across anything that questioned the themes of what I'm talking about. ... With every day that passes, you just get more information."

"If the information over a period of time does not stand up to scrutiny and fact checking, it doesn't matter how far it will circulate, it's going to be dropped," he said.

After studying conspiracy theorists, Michael Barkun, professor of political science at Syracuse University and author of the book, "Culture of Conspiracy: Apocalyptic Visions in Contemporary America," said he thought image and packaging is actually key to attracting followers.

"Even someone whose ideas are deviant can produce a Web site that looks sleek and professional," said Barkun. "Those who have conspiracy theories to peddle can do it very easily. And if they're reasonably sophisticated, [they] can do it in a way that gives those ideas the appearance of validity."

Whether those who make conspiracy theories for the masses are themselves mentally ill, Barkun said it depends on the conspiracy theorist.

"I don't think you can generalize," he said. "Certainly, in terms of conspiracy theorists, they're all quite different."

As for Icke, he has long heard people accusing him of being a mentally-disturbed conspiracy theorist.

"I went out on a limb," he said. "What's happened within a period of 20 years is that the world has come to me. ... As people have seen it coming to pass, the laughter has stopped.

"I take a different view," he added, "and if that's at odds with mainstream society to the point of being crazy, then I'm fine with that."