There's another flight simulator in Google Earth, though this time it's a little more official. You can use it to fly over 3D maps and even land on any flat area that you fancy. There are more Easter eggs in the rest of Google's properties (try typing 'Google Easter eggs' into the search box on the Google homepage, then click the 'I'm feeling lucky' button for an Easter-themed example).

Sadly, the moon in Google Maps' Google Moon isn't made of green cheese anymore, but the Gmail spam folder comes with some unique recipes. They're for SPAM rather than 'spam', but it's a tasty alternative to the usual tip or advert. We're still not sure about the SPAM kebabs, mind.

Some Easter eggs are quite subtle and can be found in plain sight. You'd need to have spent much of your life memorising movie scripts to catch all the references in World of Warcraft's character dialogue.

Similarly, the hidden emoticons in Skype's chat tools probably won't be apparent to everyone – but if you find yourself in a conversation where you're being told too much information, try typing '(tmi)' and see what happens.

If hidden games are more your thing, there's a copy of Tetris in the uTorrent bittorrent client, and Space Invaders is hidden inside OpenOffice. To play, open a new spreadsheet and add this formula to a cell: '=game()'. The cell will be filled with the text 'Say what?'. In an adjacent cell, type '=GAME("StarWars")' for a quick bout of mindless alien destruction.

Some eggs are even built into your hardware. If you've got an early Macintosh to hand, you can crack open the case to see the signatures of the entire design team on the moulding. If breaking a collectors' item isn't quite what you had in mind, you can find at least one egg on the Windows Vista DVD. Zoom in with a microscope on the copy protection hologram and you'll see a picture of one of the security team.

Then there are the Easter eggs that eventually become features of the product. Early iPods hid a copy of Breakout that became the first game installed on newer devices.

Browser eggs

Sometimes Easter eggs take a swipe at the competition. Type 'about: Mozilla' into the Firefox toolbar and you'll get a quote from the Book of Mozilla, often referring to Internet Explorer. In the latest version, Firefox 3.03, it reads:

"Mammon slept. And the beast reborn spread over the earth and its numbers grew legion. And they proclaimed the times and sacrificed crops unto the fire, with the cunning of foxes. And they built a new world in their own image as promised by the sacred words, and spoke of the beast with their children. Mammon awoke, and lo! It was naught but a follower." Firefox may not be the dominant browser in terms of numbers, but it's certainly taken the lead in setting standards.

Google's new browser, Chrome, also includes an Easter egg – but only if you're using Windows XP. It's triggered by typing an 'about' request into the toolbar – type 'about:internet' to launch the Windows Pipes screensaver inside the browser.

Vista users don't have the screensaver, so instead they get a message telling them that the tubes are clogged. It's debatable whether calling someone else's code really counts as an Easter egg, but Chrome also comes with its own eggs, including 'about:memory' and 'about:stats', which provide useful debugging information.

Internet Explorer has its own Easter eggs, though they won't work on Vista, either. You'll need to load a DLL inside IE and then edit the HTML of the blank page that appears in order to show a long scrolling list of the entire development team, along with lists of what kept them going and what they left out.