ast Tuesday, on the 18th anniversary of the lethal gas spill at a Union Carbide plant in Bhopal, India, that killed thousands of people, journalists received an e-mail press release claiming to be from Dow Chemical, which now owns Union Carbide. It was a fake, as was the Web site called up by a hyperlink in the e-mail.

The release supposedly explained why Dow refuses to clean up Bhopal or help people who remain sick from the spill. The link was to dow-chemical.com, a Web site that looked much like Dow's real Dow.com site, but that included such fake items as a "draft" of a speech by Dow's chief executive, Michael D. Parker, disavowing Dow's responsibility for Bhopal.

The hoax was the work of the Yes Men, a group of critics of business and government who gained attention in 2000 with Gatt.org, a bogus World Trade Organization site.

This time the Yes Men were too clever by at least half: they registered the site with Gandi.com in the name of James Parker, Michael Parker's real son. So the younger Mr. Parker took ownership, and Dow took the site down last Wednesday night.

"We thought it would be funny, but it turned out to be stupid," said Andrew Bichlbaum, a Yes Men volunteer in Paris who set up the site. "We gave them the chance to claim the site as their property."

The Yes Men resurrected the site on Friday, as dow-chemical.va.com.au, whose host is Virtual Artists, an Australian company. Any visitor can download a copy of the site, Mr. Bichlbaum said, "so that if Dow gets this one too, it will continue to exist."

Although no other environmental group has acknowledged participation in the hoax, at least one voiced approval. "We support the people who published this site," said Casey Harrell, the Bhopal specialist at Greenpeace, one of Dow's most vocal critics.

Dow, meanwhile, maintains that the Web site violated numerous cyberspace copyright laws.

"It is ironic," said John Musser, a Dow spokesman, "that groups that position themselves as public defenders against companies that act irresponsibly, unethically or unlawfully are turning out to be the poster children for those very behaviors."