We all like to poke fun at whether some feature in a product was was a flaw, or if it was a desired effect. Of course much of this depends on perspective, for instance, there may be as many attackers that will swear by macros in popular office software as there are those who used it's intended functionality to do their daily work. Or even the common misconceptions about aluminium foil, and it's reflective vs dull sides. Or whether or not a DoS is protecting your users by failing closed, or destroying your business by restricting access. In this highly interactive talk that will involve the audience weighing in with their votes, I'd like to go through some historical and current completely unexpected bugs that became critical features, and some amazing features that became critical bugs. Of course there is a LOT of grey area that one could…speculatively execute…with the topic so we'll also contemplate everything in between.