Writing buggy applications is a cinch--for decades, the world's software developers have been proving that with just about every program they release. Truly interesting bugs, however, are a relatively rare breed. I'm talking about the kind that cause technology products and services to stop working for extended periods, or that prompt them to behave as if they were possessed or harbored grudges against the humans who use them. And even though the bugs themselves usually stem from mundane errors such as typos or faulty math, their symptoms are anything but boring.

For this story, I rounded up nine truly peculiar bugs that bedeviled customers of some of the largest providers of software and services on the planet. (I didn't cover ones with catastrophic side effects such as explosions or the death of human beings; Simson Garfinkel discusses some of those in this creepy good read at Wired.com. Of course, when it comes to bugs, Windows occupies a category of its own, as you'll see in "The Worst Windows Flaws of the Past Decade." And sometimes the problem isn't a mistake so much as a really bad idea from the beginning; see "The 25 Worst Tech Products of All Time" and "The 10 Dumbest Tech Products So Far.")

I began my research intending to cover the whole PC era, but I quickly discovered that most of the strangest bugs have appeared in recent years. As a matter of fact, the three wackiest ones in my list--involving Google's Android OS, Microsoft's Zune, and Google itself--all cropped up in just the past few months. I'm not sure if software is getting buggier, but I am pretty certain that bugs are getting weirder.

Our first bug, however, dates from a simpler time. One in which it didn't occur to software companies to do things like encrypt intensely sensitive information...

1995: Many Unhappy Returns

The bizarre symptom: Intuit's MacInTax (a program later replaced by TurboTax) was designed to let Mac users file their taxes. But the version for the 1994 tax season had another feature, discovered by one taxpayer: It allowed any customer with a little telecommunications knowledge to dial in to a computer where 60,000 tax returns sat unprotected. Once in, a user could view any return, make changes, or simply erase the return entirely.

The bug: MacInTax was bundled with a debug utility intended to help customers diagnose modem problems. The utility dialed in to a server operated by an Intuit subcontractor. The utility used an account name and password that weren't encrypted or otherwise obscured, and that granted anyone who stumbled across them complete access to MacInTax users' data. Intuit called the glitch "an oversight"--no kidding!--and apologized. The company offered to pay any penalties suffered by anyone whose return encountered problems as a consequence.

1998: Auction Interruptus

The bizarre symptom: On June 10, eBay--then, as now, the world's dominant online auction site--suffered an outage. Nothing remarkable about that: Throughout the late 1990s, the company's sellers and bidders frequently faced unscheduled downtime. But this outage just kept going and going. By the time the site recovered on June 11, 22 hours had passed and 2.3 million auctions in progress were compromised, forcing eBay to waive a small fortune in fees.

The bug: eBay blamed the meltdown on a corrupted database, and it blamed the corrupted database on buggy Sun Microsystems software. Fourteen months later, the site had a 14-hour outage that was nearly as embarrassing and costly; that time, the company said that hardware problems were to blame.

2005: Surprise Ending

The bizarre symptom: Did you ever suspect that TiVo's mascot--a tiny anthropomorphic TV with a lopsided grin--has a sadistic side? You might have if you owned one of the company's DVRs back in late 2005. That was when couch potatoes began to notice that their TiVos were randomly chopping large chunks off the end of shows, turning many a program with a suspenseful conclusion into a permanent cliffhanger.

The bug: The company took a while to respond, but eventually it concluded that the truncated recordings affected only Series 2 TiVos that had been running continuously for extended periods. Initially it advised owners to power their DVRs off and then on again occasionally, and later it issued a patch designed to eradicate the problem permanently.

2006: Game Over

The bizarre symptom: You could say that Bubble Bobble Revolution, a Nintendo DS remake of the 1980s arcade classic Bubble Bobble, was a surprisingly tough game. Level 30, for instance, was unbeatable--literally. That was a trifle odd given that the game boasted a total of 100 levels.

The bug: As in many arcade-style games, Bubble Bobble Revolution levels ended by challenging the player to defeat an überenemy, known as a boss. But level 30 had no boss to defeat, and therefore no way to continue to level 31. Months later, publisher Codemasters replaced defective cartridges with a debugged version--and threw in another game, Rainbow Islands Revolution, by way of apology.