Of course, the warning would have appeared as an image, rather than text embedded in the site, which should have set alarm bells ringing - except that, as soon as news of the warning came out, the website collapsed under the sheer number of people trying to log onto the site.

BBC: Was the 'gunman warning' a hoax?

The red Fire Warning light is bad news when it lights up, but you can silence the alarm bell by pressing it.

FORBES: What Do All The Controls In An Airplane Cockpit Do?

"If people see a warning a lot, but then nothing bad happens in the average case, it decreases the alarm level" and people won't pay attention even when they need to, said Adrienne Porter Felt, a Ph.

WSJ: Selling You on Facebook