Easter eggs

A virtual Easter egg is an intentional hidden message, in-joke or feature in a work such as a computer program webpage, video game,  movie, book or crossword. The term was coined—according to Warren Robinnet by Atari after they were pointed to the secret message left by Robinett in the game adventure. It draws a parallel with the custom of the easter egg hunt observed in many western nations as well as the last Russian imperial family's tradition of giving elaborately jeweled egg-shaped creations by Cark Faberge which contained hidden surprises.

This practice is similar in some respects to hidden signature motifs such as Diego Rivera including himself in his murals, Alfred Hitchocks legendary cameo appearances, and various " Hidden Mickeys" that can be found throughout the various Disney Parks. An early example of this kind of "Easter egg" is Al Hirschfeld`s Nina.

Atari's Adventure, released in 1979, contained what was thought to be the first video game "Easter egg", the name of the programmer Warren Robinnet. However, evidence of earlier Easter eggs has since surfaced. Several cartridges for the Fairchild Channel include previously unknown Easter eggs, programmed by Michael Glass and Brad Reid-Selth, that are believed to predate Robinett's work.

Some important easter eggs are:

In Google Reader:
If you click ↑ ↑ ↓ ↓ ← → ← → BA (Konami code) Sidebar background color change to blue, and include a picture of a ninja.

In Mozilla Firefox:
If you type about: mozilla in the address bar, you see a passage from The Book of Mozilla.
 

In Firefox 3, if you type about: robots into the address bar, you see a pet robot greeting application, accompanied by quotations related to robots from various books or science fiction films.

In Google Chrome:
If you type about: internets into the address bar, you'll see an animation of pipes (you need to have the pipes installed wallpaper).

Google
Google easter eggs if you type in the search box, and then click I'm feeling lucky, you see a game.

In Adobe Photoshop:
In the dialog "About" if you press CTRL + SHIFT, you'll see a different image to regular dialogue, which vary by program.