A word of caution about editing entries "anonymously" in Wikipedia: a tool has been developed that can show who made the changes.

Virgil Griffith, who will be a graduate student at the California Institute of Technology starting in September, has developed Wikipedia Scanner, a search tool that traces the IP address of people who make edits to the online encyclopedia.

While Wikipedia allows anyone to make edits, it keeps detailed logs of the changes made. And although people can make changes without identifying themselves, the changes often create digital fingerprints that provide information about the user, such as the location of the computer used to make the edit.

Many of the edits detected by the scanner correct spelling mistakes or obvious factual errors, but others have been used to polish entries by rewriting or removing critical material. The scanner has traced entries to people at several large companies who appear to have altered potentially damaging content.

Someone on Wal-Mart Stores' network, for instance, altered a line about the wages it pays employees. The original entry stated that "Wages at Wal-Mart are about 20% less than at other retail stores," citing the author Greg Palast as the source. The revised entry reads: "The average wage at Wal-Mart is almost double the federal minimum wage," and changes the attribution to Wal-Mart.

A person with access to an IP address at the election systems division of Diebold cut large sections out of an entry about concerns of security experts over the integrity of Diebold's voting machines, as well as information about the its CEO's fundraising for President George W. Bush. The deleted text was later restored.

And a user of a computer at the British Broadcasting Corp. changed Bush's middle name from "Walker" to "Wanker."

The scanner has also tracked digital fingerprints that have led to computers at the Central Intelligence Agency and the Vatican.

Griffith created the tool to "create minor public relations disasters for companies and organizations I dislike," he wrote on his Web site. He admitted that it's impossible to be sure if the edits were made by someone working at one of the organizations, although the IP address reveals that they were made by someone with access to their network, he says.

"If the edit occurred during working hours, then we can reasonably assume that the person is either an agent of that company or a guest that was allowed access to their network," he wrote.

Griffith came up with the idea when he "heard about Congressmen being caught for white-washing their Wikipedia pages," he said.

He said he believes that anonymous speech is important for open projects such as Wikipedia. The online encyclopedia works fine today for "noncontroversial topics," he said, but tools such as Wikipedia Scanner can help make the site more reliable for controversial topics, he said.

A spokesman for Wikipedia in Germany referred to the scanner tool as a "good development" and encouraged other researchers and people to download data from the online encyclopedia and snoop around. "There's surely plenty to discover," he said via e-mail.