More than 10 million people visit the unofficial encyclopedia Web site Wikipedia daily looking for information.
The site, which debuted in January 2001, allows almost anyone to edit entries, but for the first time the public has learned where some of the changes are coming from.
Now the site, which bills itself as the largest knowledge resource in the world, has a way to track down those who edit content.
Virgil Griffith, 24, wrote a program Wikiscanner that can match edits to Wikipedia entries to the computer networks from which they come.
"Companies are trying to manipulate things if they can," Griffith said. "As for the CIA, they added very large sections. Another one is congressmen whitewashing their pages, so they will remove things like campaign promises."
His program found that someone at a Wal-Mart computer apparently had changed a line. It used to say wages at Wal-Mart were 20 percent less than other stores. The new entry says the average wage at Wal-Mart is double the minimum wage.
Another entry with a questionable change came on conservative commentator Rush Limbaugh's entry. When someone from a Democratic Party computer edited his entry, he went from a "popular" entertainer and talk show host to an "idiotic" one.
Last year Wikipedia founder Jimmy Wales said that the site wanted people to participate and that he began the site to offer free knowledge to anyone.
"We value openness," Wales said. "We value participation. But openness and participation can take a lot of different forms."
Wikipedia has always restricted changes to a small percentage of articles and volunteer administrators, according to a report in The New York Times.
Wales also suggested that the identities of people who edit content may not necessarily be hidden.
"People should understand you are not necessarily as anonymous as you think," he said.