ACCORDING to Wikipedia, the online encyclopedia, John Seigenthaler Sr. is 78 years old and the former editor of The Tennessean in Nashville. But is that information, or anything else in Mr. Seigenthaler's biography, true?
The question arises because Mr. Seigenthaler recently read about himself on Wikipedia and was shocked to learn that he "was thought to have been directly involved in the Kennedy assassinations of both John and his brother Bobby."
"Nothing was ever proven," the biography added.
Mr. Seigenthaler discovered that the false information had been on the site for several months and that an unknown number of people had read it, and possibly posted it on or linked it to other sites.
If any assassination was going on, Mr. Seigenthaler (who is 78 and did edit The Tennessean) wrote last week in an op-ed article in USA Today, it was of his character.
The case triggered extensive debate on the Internet over the value and reliability of Wikipedia, and more broadly, over the nature of online information.
Wikipedia is a kind of collective brain, a repository of knowledge, maintained on servers in various countries and built by anyone in the world with a computer and an Internet connection who wants to share knowledge about a subject. Literally hundreds of thousands of people have written Wikipedia entries.
Mistakes are expected to be caught and corrected by later contributors and users.
The whole nonprofit enterprise began in January 2001, the brainchild of Jimmy Wales, 39, a former futures and options trader who lives in St. Petersburg, Fla. He said he had hoped to advance the promise of the Internet as a place for sharing information.
It has, by most measures, been a spectacular success. Wikipedia is now the biggest encyclopedia in the history of the world. As of Friday, it was receiving 2.5 billion page views a month, and offering at least 1,000 articles in 82 languages. The number of articles, already close to two million, is growing by 7 percent a month. And Mr. Wales said that traffic doubles every four months.
Still, the question of Wikipedia, as of so much of what you find online, is: Can you trust it?
And beyond reliability, there is the question of accountability. Mr. Seigenthaler, after discovering that he had been defamed, found that his "biographer" was anonymous. He learned that the writer was a customer of BellSouth Internet, but that federal privacy laws shield the identity of Internet customers, even if they disseminate defamatory material. And the laws protect online corporations from libel suits.
He could have filed a lawsuit against BellSouth, he wrote, but only a subpoena would compel BellSouth to reveal the name.
In the end, Mr. Seigenthaler decided against going to court, instead alerting the public, through his article, "that Wikipedia is a flawed and irresponsible research tool."
Mr. Wales said in an interview that he was troubled by the Seigenthaler episode, and noted that Wikipedia was essentially in the same boat. "We have constant problems where we have people who are trying to repeatedly abuse our sites," he said.
Still, he said, he was trying to make Wikipedia less vulnerable to tampering. He said he was starting a review mechanism by which readers and experts could rate the value of various articles. The reviews, which he said he expected to start in January, would show the site's strengths and weaknesses and perhaps reveal patterns to help them address the problems.
In addition, he said, Wikipedia may start blocking unregistered users from creating new pages, though they would still be able to edit them.
The real problem, he said, was the volume of new material coming in; it is so overwhelming that screeners cannot keep up with it.
All of this struck close to home for librarians and researchers. On an electronic mailing list for them, J. Stephen Bolhafner, a news researcher at The St. Louis Post-Dispatch, wrote, "The best defense of the Wikipedia, frankly, is to point out how much bad information is available from supposedly reliable sources."
Jessica Baumgart, a news researcher at Harvard University, wrote that there were librarians voluntarily working behind the scenes to check information on Wikipedia. "But, honestly," she added, "in some ways, we're just as fallible as everyone else in some areas because our own knowledge is limited and we can't possibly fact-check everything."
In an interview, she said that her rule of thumb was to double-check everything and to consider Wikipedia as only one source.
"Instead of figuring out how to 'fix' Wikipedia - something that cannot be done to our satisfaction," wrote Derek Willis, a research database manager at The Washington Post, who was speaking for himself and not The Post, "we should focus our energies on educating the Wikipedia users among our colleagues."
Some cyberexperts said Wikipedia already had a good system of checks and balances. Lawrence Lessig, a law professor at Stanford and an expert in the laws of cyberspace, said that contrary to popular belief, true defamation was easily pursued through the courts because almost everything on the Internet was traceable and subpoenas were not that hard to obtain. (For real anonymity, he advised, use a pay phone.)
"People will be defamed," he said. "But that's the way free speech is. Think about the gossip world. It spreads. There's no way to correct it, period. Wikipedia is not immune from that kind of maliciousness, but it is, relative to other features of life, more easily corrected."
Indeed, Esther Dyson, editor of Release 1.0 and a longtime Internet analyst, said Wikipedia may, in that sense, be better than real life.
"The Internet has done a lot more for truth by making things easier to discuss," she said. "Transparency and sunlight are better than a single point of view that can't be questioned."
For Mr. Seigenthaler, whose biography on Wikipedia has since been corrected, the lesson is simple: "We live in a universe of new media with phenomenal opportunities for worldwide communications and research, but populated by volunteer vandals with poison-pen intellects."