A libertarian thinktank devoted to rubbishing climate change is threatening to sue anybody commenting on certain leaked documents - even where the papers are genuine, it says.
Internal documents belonging to the Heartland Institute were leaked to the DeSmogBlog website, and appear to show the extent to which the Insitute's activities are funded by major corporations, some of which publicly support action on climate change.
In other material, a $100,000 program to try and stop teachers teaching science is supposedly revealed.
The documents say the program's designed to "show that the topic of climate change is controversial and uncertain – two key points that are effective at dissuading teachers from teaching science."
But in an extraordinary statement on its website, the Heartland Institute is fighting back.
First, it says, some of the documents 'may have been' altered - but the Institute says it hasn't actually had time to check. One, it claims, is a complete fake: 'Confidential Memo: Heartland Climate Strategy'. But even those which it admits are genuine mustn't be discussed, it says.
"The individuals who have commented so far on these documents did not wait for Heartland to confirm or deny the authenticity of the documents," it says.
"We believe their actions constitute civil and possibly criminal offenses for which we plan to pursue charges and collect payment for damages, including damages to our reputation. We ask them in particular to immediately remove these documents and all statements about them from the blogs, Web sites, and publications, and to publish retractions."
Much of the material, though, it admits is genuine, including the list of donors - indeed, it's apologized to the donors whose identities were revealed.
"We promise anonymity to many of our donors, and we realize that the major reason these documents were stolen and faked was to make it more difficult for donors to support our work," it says.
These donors include major tobacco firms as well as General Motors and drinks company Diageo - although most of these donations were made for purposes other than ant-climate change lobbying.
However, much of the group's funding appears to have come from a single anonymous donor, who's contributed several million dollars in the last few years.
The Heartland Institute admits that the documents were sent to DeSmogBlog by a staffer who thought they were going to a board member.