From The Wikipedia.org: The Yes Men are a group of culture jamming activists who practice what they call "identity correction". They pretend to be powerful people and organizations and then use their newfound authority to espouse what they think those groups really believe, or in some cases what they think the groups should believe. Its two leading members are Andy Bichlbaum and Mike Bonano, but they are assisted by numerous people across the globe.
The Yes Men's most famous prank is placing a "corrected" WTO website at gatt.org (GATT is the treaty that led to the WTO). The fake site began to receive real emails from confused visitors, including invitations to address various elite groups on behalf of the WTO, which they obligingly took up. More