You may have seen a cautionary message on Facebook over the past few days, warning you to repost some legalese or risk sacrificing your almighty privacy to the social network.

Alternately, you may have seen it toward the beginning of December. Or in June 2012. Or at innumerable other random times over the course of the past three years.

The Facebook warning hoax, you see, is a very special and pernicious kind of hoax — the kind that flares back up long after it’s been debunked once and for all.

To briefly surmise the work of a thousand previous debunkers: No, Facebook does not own the copyright to everything you post; no, posting a gibberish “statement” about your “rights” doesn’t actually establish them or override Facebook’s Terms of Service; yes, you are an idiot if you fell for this … again.

How does that happen, exactly? Misinformation runs rampant on the Internet, as we know, but this type of long-lived, recurring hoax is a more unusual breed. Aside from versions of the Facebook copyright/privacy hoax, which appear to have started in earnest in 2012, there’s a running gag about a “day without gravity,” which dates back to the 1970s, and a very regular, 12-year-old hoax about Mars, which claims it will — for one day! — appear as big as the moon. (NASA has been refuting that one for years.)

At some point, you can’t even call these things hoaxes anymore because they’re always in the background, like some stubborn folk superstition, just waiting to bubble up in the mainstream again. In fact, psychologist Stuart Vyse classifies chain messages as a form of superstition.

After all, just like lucky charms, legends like the recurring Facebook message promise to ward off things that we fear or don’t understand: vast corporations, complex copyright laws, the looming specter of big data and disappearing privacy. That a status update could protect against those things makes no sense, of course, but it vindicates and comforts whatever vague anxieties we feel.

“These narratives are believed because they construct and reinforce the worldview of the group within which they are told, or because they provide us with coherent and convincing explanations of complex events,” media scholar Dylan McLemore wrote of chain e-mails in 2011.

In other words, people keep posting that ridiculous Facebook warning because they don’t understand Facebook. A “privacy notice,” no matter how dubious, is at least something they can swallow.

And it means we’ll probably see the Facebook hoax again. And again. And again.