Page last updated at 16:50 GMT, Thursday, 9 April 2009 17:50 UK

Hunting Easter eggs in software

Tom Royal from Computer Active magazine
Tom Royal says Easter eggs are a chance for developers to show off

Easter eggs are not just made of chocolate. With a bit of perseverance they can be found hidden inside DVDs, games and even business software.

Computer code with a hidden purpose can be found lurking beneath DVDs, video games, and software such as spreadsheets, or word processors, Marc Cieslak found out.

The secret add-ons are often little jokes or tips-of-the-hat by programmers who have slaved for months and even years over a piece of software.

"Show off"

Easter eggs have been around since the dawn of personal computing and often take the form of a hidden credits list to programming teams.

"Historically Easter eggs are just a chance for software programmers to really show off what they can do," said Tom Royal from Computer Active magazine.

"Quite often they are working on quite dull office products and it's their way of getting their names in the finished product," he added.

Google bunny
Google has an Easter egg bunny for users of its search engine

Peeling away the layers of an application by using arcane key combinations can reveal hidden content in some unlikely places.

Microsoft's Excel 97 contained a weird psychedelic flight simulator which led the user to a black monolith down which scrolled the names of the programming team.

Excel 2000 went a step further by hiding an arcade style driving game in the code of its spreadsheets.

Plus, typing "Google Easter eggs" into the search engine of the same name and hitting the "I'm Feeling Lucky" button takes uses to an Easter themed game.

Bonus material

It has been a long held practice that video games contain content that the player is supposed to discover for themselves.

In Grand Theft Auto 4, take a helicopter ride over to the statue of happiness, jump out and look for a doorway.

If the player ignores the signs and enters the structure, the statue's beating heart can be found after a long climb.

Call of Duty 5: World at War contains an entirely new game - just complete the single player campaign mode to unlock a creepy zombie shooter.

Excel 2000's hidden game
Excel 2000 has a hidden game within the program

The film world has embraced the notion of the Easter egg too - some secret and special bonus material can often be found in DVDs hidden in among the production notes and photo galleries.

Hardware features

But accessing Easter eggs on DVDs can be a real test of the film lover's patience because these may require pressing the right sequence of keys on menu screens or hitting the play button at a certain time.

However, persevering through trial and error could reveal bonus material such as outtake reels, more behind-the-scenes features, or even entire re-edits of films.

Occasionally the odd hidden feature exists in hardware too - Nokia's N95 mobile phone has a little-known accelerometer that can enable motion controlled applications.

It can be activated by downloading a plug-in from the Nokia research website. This means the handset can used for motion sensitive applications, for example as a pedometer.

Prospective Easter egg hunters are unlikely to just stumble across many of these hidden items.

But there are many online guides with detailed instructions on accessing hidden content.

The BBC is not responsible for the content of external internet sites

Has China's housing bubble burst?
How the world's oldest clove tree defied an empire
Why Royal Ballet principal Sergei Polunin quit

banner watch listen bbc sport Americas Africa Europe Middle East South Asia Asia Pacific