In general, changes to a Wikipedia page cannot be traced to an individual, only to the owner of a particular network. In 2004, someone using a computer at ExxonMobil made substantial changes to a description of the 1989 Exxon Valdez oil spill in Alaska, playing down its impact on the area’s wildlife and casting a positive light on compensation payments the company had made to victims of the spill.

Gantt Walton, a spokesman for the company, said that although the revisions appeared to have come from an ExxonMobil computer, the company has more than 80,000 employees around the world, making it “more than a difficult task” to figure out who made the changes.

Mr. Walton said ExxonMobil employees “are not authorized to update Wikipedia with company computers without company endorsement.” The company’s preferred approach, he said, would be to use Wikipedia’s “talk” pages, a forum for discussing Wikipedia entries.

Mr. Wales also said the “talk” pages are where Wikipedia encourages editors with a conflict of interest to suggest revisions.

“If someone sees a simple factual error about their company, we really don’t mind if they go in and edit,” he said. But if a revision is likely to be controversial, he added, “the best thing to do is log in, go to the ‘talk’ page, identify yourself openly, and say, ‘I’m the communications person from such and such company.’ The community responds very well, especially if the person isn’t combative.”

Mike Sitrick, a longtime public relations consultant in Los Angeles, agreed. “I’m a big believer that if you’re going to correct it, correct it with a name,” he said. “Otherwise it hurts your credibility.”

An Anheuser-Busch employee eventually took responsibility for the changes to the SeaWorld page  but only after being challenged about them twice by another user. A person identifying himself as Fred Jacobs, communications director for the company’s theme park unit, said on the entry’s “talk” page that discussion of the ethics of keeping sea creatures captive “belongs in an article devoted to that subject.”