There's no such thing as a secret online

There's a truism that I like to share with as many people as possible: if you don't want other people to see something, then don't post it online. It is, you might think, a pretty simple concept to grasp. After all, you wouldn't stroll into a bar with a megaphone and yell "I'm not wearing underwear" if you wanted to keep that secret would you? But would you write that fact down on small pieces of paper and slip them unnoticed into the pockets of people in that bar if you wanted to reveal all (please excuse the unfortunate choice of phrase) without revealing your identity? In a nutshell, that's what apps such as Secret promise to do; but such a promise of anonymity is always going to be hard to deliver.