The first worm to infect the iPhone will not affect most users of Apple's smartphone, despite worrying reports. The ikee worm only affects jailbroken iPhones, representing a minority percentage of iPhones on the market.

Reports this weekend warned of a number of iPhones in Australia reportedly infected by a worm that only replaces the device's background wallpaper with an image of 80's pop icon Rick Astley.

According to security firm Sophos, the worm attempts to find another jailbroken iPhone on the mobile phone network and install itself. However, there have been no confirmed reports of infections outside Australia's territory.

What needs to be stressed though, is the fact that the ikee worm only affects jailbroken iPhones running the SSH app with the default password, which represents a very small percentage of the total number of iPhones out there. Even those who have jailbroken iPhones can easily change the root password, which should ward off such an attack.

Jailbreaking an iPhone (with tools such as purplera1n) removes Apple's protection mechanism, allowing the phone to run any software outside the company's own App Store, including nasties such ikee.

Apple condemns jailbreaking and doing so to an iPhone will void the device's warranty. The Cupertino company is cracking down on iPhone jailbreakers and is already reported to ship new jailbreak-proof 3GS models. Apple is also hiring security specialists to tackle to problem, according to reports.

Meanwhile, security experts say that as long as your iPhone is not jailbroken, you should be safe from the ikee worm. If you do use a jailbroken iPhone, you can use these instructions to protect your phone.

However, F-Secure warns that malicious variants of ikee could soon follow. The worm's creator released the full source code of this worm and other could develop more variants that could have a more damaging payload than just changing the phone's wallpaper.