The internet is constantly, relentlessly public. Post something and it's there, for everyone, all the time.
Acar has come up with a clever idea, a small idea that makes things just a little protected. Trick.ly is a url shortener with a twist. You can share a URL but hide it behind a question that only insiders can easily answer.
So, for example, you could tweet, "Here's the source for my world-class chili: http://trick.ly/2L5". Anyone can go there, but only people who can figure out the clue can discover the site you were pointing to.
It's not secure. It's sort of private. Neato.