Once more, pop sensation Rick Astley is sweeping the nation. Only this time, the nation is Australia, and he's starring not on the tube, but on Apple's (NASDAQ:AAPL) iPhone.

Astley's mug is appearing on iPhones Down Under thanks to ikee, an invasive bit of software code that installs a photo of the pop singer on a vulnerable handset and then establishes it as the default wallpaper with the message, "ikee is never going to give you up," eWEEK reports. RickRolling has never been so insidious.

What looks like a joke could quickly become a problem for those who've used software to free their iPhones to work with any carrier they choose, a process called "jail-breaking." Only jail-broken iPhones are suffering from the ikee worm.

If this seems like good news for Apple, trust me, it isn't. But I understand why some would think it is. Each time a worm affects an unauthorized iPhone, it argues for the safety and comfort of preferred providers such as AT&T (NYSE:T) here in the U.S.

The problem with this argument is that there are some users who loathe AT&T enough to cut the umbilical. And not just AT&T; jailbreaking is a worldwide phenomenon. China Unicom (NYSE:CHU), an authorized iPhone partner, badly trails China Mobile (NYSE:CHL), whose network could be serving as many as 1 million jailbroken iPhones.

Hackers have to like those numbers. My guess is they'll soon be targeting gray-market iPhones with worms designed to steal, rather than prank.

Where does this leave Apple? Stuck. The Mac maker can't reasonably be asked to support iPhones that aren't under warranty. But imagine what happens if worms become sophisticated enough to jump from jail-broken iPhones to more legit models. Apple needs to get ahead of this issue before it becomes a selling point for Palm (NASDAQ:PALM), Research In Motion (NASDAQ:RIMM), or even Dell (NASDAQ:DELL).

We're starting to talk as if Apple has created the Windows of the wireless world via the iPhone and its App Store. Now, hackers are starting to act like it.

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Fool contributor Tim Beyers had stock and options positions in Apple at the time of publication. Check out Tim's portfolio holdings and Foolish writings, or connect with him on Twitter as @milehighfool. The Motley Fool is also on Twitter as @TheMotleyFool. The Fool's disclosure policy has never once lived in a van down by the river.