According to Wikipedia,
An Easter egg is an intentional inside joke, hidden message, or feature in a work such as a computer program, movie, book, or crossword.
We all know what that means in the context of a film (no children’s film seems complete without multiple references to nostalgic films to keep the grown-ups awake), but have you ever come across an Easter egg in a software program? It’s a hidden gem that pops up only in response to a specific set of commands, and which is not included in the software manual. In a game this might give you an extra life or level, it might produce an unexpected message on-screen, or it might even be a feature completely unconnected to the original program, such as the pinball game included in the 1997 version of Microsoft Word.
This RadiantMinds article suggests that Easter eggs originate with developers wanting to sign their work. Both Bill Gates and Steve Jobs have blown hot and cold on Easter eggs, possibly because in the context of giving credit to individual software programmers, it enabled the competition to know whom to lure lure away. Gizmodo adds that it really all begins with the Russian royal family, which concealed surprises within Fabergé eggs.
Surprises aren’t always nice, though. What if an Easter egg, by its nature hidden from everyone, contains something designed to damage, rather than to amuse? This AVAST! blog article approaches just that subject, with Filip Chytrý of the AVAST! Virus Lab. Chytrý makes the very good distinction that an Easter egg reacts in response to the user’s input, whereas malware simply operates on its own.
Where to find them
You want to find a few Easter eggs now, don’t you? The RadiantMinds article is worth a read as it includes a few classics. This Choice article also includes a list of Easter eggs, including a nifty one for Android. Easter eggs even pop up in hardware such as circuit boards.
If you think you know your Easter eggs, how about taking TechWeek’s Easter egg quiz?