These days, software engineers’ overlords generally don’t tolerate true, secret Easter eggs. The bosses argue that such surprises are untested, may be incompatible with the software company’s public image, and (when they feature the programmers’ names) amount to “poach me!” ads for rival companies’ headhunters. In other words, the heyday of software Easter eggs has passed.

But about 15 years ago, programmers used to put their personal pawprints all over their work, buried, sometimes devilishly, as hard-to-unlock surprises.

It’s too bad. There are a few great jokes left in software, but nothing like some of the classics of yesteryear. Here are a few of the best.

* Iguana-Spangled Banner. On PCI-slot Power Macs (circa 1998) running System 7.5.5 through 7.6.1, an astonishing Easter egg appeared if you opened Notepad, typed secret about box, and then dragged that text to the desktop. Suddenly, your screen changed to a computer-generated, 3-D picture of Apple’s headquarters—with a flag flapping in the foreground. It showed an iguana and the legend “iguana iguana powersurgius” (PowerSurge was the code name for Macs with PCI slots).

You could control the direction of the flag-waving by moving your mouse. In fact, if you jerked the mouse up and down hard enough, you could even rip the flag off the pole, and watch it flutter away into the distance.

Even that was just the start. Holding down letter keys triggered special effects, like substituting a photo of the programmers for the iguana, calling up a display of the animation’s frame rate, or showing your cursor coordinates.

They don’t make Easter eggs like that anymore.

* The Office 97 flight simulator. If you opened Excel 97 and created a new blank document, pressed F5, typed X97:L97 into the box and then pressed Enter and Tab, you’d jump to cell M97. If you then Control-Shift-clicked the Chart Wizard button, you’d trigger an actual flight simulator. (Not much chance of stumbling on that one by accident.)

You could control your flight using the mouse to steer; you’d click the right mouse button to fly forward, left button for reverse. You’d end the game by pressing Control+Shift+Escape.

* Quark the Alien. In QuarkXPress, versions 3.1 through 8, an entertaining secret animation awaited if you created an object (like a picture or text box) and then pressed Command-Option-K. A hilarious-looking cartoon alien emerged from the edge of the screen, clomped out into the middle of your document, aimed his raygun, and then blasted your text box or picture into oblivion.

* The Photoshop cat belch. In Photoshop for Macintosh version 4, if you held down the Command key while you chose About Photoshop from Apple menu, you’d get a photo of a big electric cat. If you then clicked the cat’s nose while pressing Command key, the cat opened its mouth and emitted a gurgly, resonant burp.

* The Photoshop dominatrix cat. In Photoshop for Windows version 6, hold down Ctrl+Alt as you open the Help menu and choose About Photoshop. The resulting screen depicts “Venus in Furs,” a cat with a whip. (“Venus in Furs” was a book by Austrian author Leopold von Sacher-Masoch in 1870; from his name, we get the term “masochist.”)