People have been complaining for a while that passing a CAPTCHA is too difficult, but developer and tech CEO Guillermo Rauch has made one of the hardest yet: a fully playable CAPTCHA based on the classic PC game Doom. It's been a long-running joke that developers will make Doom run on absolutely anything, so it's not much of a surprise that it's now running inside something that resembles a CAPTCHA. The app essentially amounts to a small Doom level that is playable with keyboard controls (arrow keys to move, space bar to shoot) within a CAPTCHA-like presentation.