Twitter’s “Don’t Click” prank, explained
Human nature being what it is, many people clicked the button, which
seemingly did nothing. What it actually did, though, was put your Twitter
home page on top of the button as a frame, with an opacity of 0 in the CSS.
The update field was pre-set with the tweet pointing to the page. The
following screenshot makes this obvious, with the opacity set here to 0.5: