“Here's an amazing talk by Rob Pike where it's casually mentioned, for example”
Rob Pike talk that mentions the Crabs prank program.
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Crabs was probably the first graphical prank program—most assuredly the first well-documented one: there are a lot of scattered anecdotes about it around. Here's an amazing talk by Rob Pike where it's casually mentioned, for example: this video It's not something you see very often anymore, partially because modern windowing systems (and systems in general, really) were built with different security models in mind (you can probably remember a few similar programs released into the wild for real mode operating systems, they were especially common then), but also because windowing systems have moved away from how simple UNIX's windowing system was at the time. It's actually kind of relevant to something that was on the front-page recently: the displays they were using (JERQ/Blit bitmap displays) depended on a routine that Larry Tesler co-invented (the bit blit, hence the name "Blit"). link link If you want to give it a try, I think 9front ships with a Blit emulator these days; load up v8 and you should have a nice few hours poking around. link