Apple iPhone owners in Australia have reported that their smart phones have been infected by a worm that has changed their wallpaper to an image of 1980s pop crooner Rick Astley.

The worm, which could have spread to other countries although there are no confirmed reports outside Australia, is capable of breaking into jail broken iPhones if their owners have not changed the default password after installing SSH. Once in place, the worm appears to attempt to find other iPhones on the mobile phone network that are similarly vulnerable, and installs itself again

On each installation, the worm - written by a hacker calling themselves "ikex" - changes the lock background wallpaper to an image of Rick Astley with the message:

ikee is never going to give you up

What's clear is that if you have jail broken your iPhone or iPod Touch, and installed SSH, then you must always change your root user password to something different than the default, "alpine". In fact, it would be a good idea if you didn't use a dictionary word at all.

The worm will not affect users who have not jail broken their iPhones or who have not installed SSH.

SophosLabs is analyzing the worm's code, which suggests that at least four variants have been written so far. One of the attributes of the latest variant (labeled the "D" version) is that it tries to hide its presence by using a file path suggestive of the Cydia application.

Presently it appears that the worm does nothing more malicious than spread and change the infected user's lock screen wallpaper. However, that doesn't mean that attacks like this can be considered harmless.