Facebook users have begun posting a 'notice' that their content is copyrighted - in the mistaken belief that this protects their images and posts from Facebook and its advertisers.
But the message is a hoax - a variation on a theme which has circulated before - and offers no protection at all.
The post, which is circulating widely on the social network, is in response to the site's announcement last week that it was to scrap voting on its privacy policies for its one billion users.
The text says, "In response to the new Facebook guidelines I hereby declare that my copyright is attached to all of my personal details, illustrations, comics, paintings, professional photos and videos, etc. (as a result of the Berner Convention).
"For commercial use of the above my written consent is needed at all times!"
But merely saying that content is copyrighted does NOT offer legal protection against Facebook.
Users have already agreed to the site's privacy policies by signing up.
Facecrooks, a popular 'scam-watching' site, says, "The bogus Privacy Notice is making the rounds again. The message is totally worthless.
"Your Facebook data is governed by its Data Use Policy, and FB cooperates with law enforcement and government agencies.
"Simply posting a status update offers you no protection whatsoever."
Facebook announced last week that it was to scrap a process that allowed the site's one billion users to vote on changes to its privacy policies.
Elliot Schrage, Vice-President of Communications said, "We’re proposing to end the voting component of the process in favor of a system that leads to more meaningful feedback and engagement."
The announcement has drawn more than 16,000 comments.