True story. I download the ROT13 extension for BBEdit (A Macintosh text editing program) from an FTP site. The idea is simple. I install the extension, select a section of text, and with a simple command it executes the ROT13 algorithm on the text. Except that I got a dialog box saying: "ROT13 is not undoable! Do you still wish to proceed?(Yes)(No)" Just imagine, I could have ROT13-ed my entire file and not be able to get the original back!! Boy am I happy my computer is smart enough to warn me...
(From the "Rest" of RHF)