Security firms have located the first iPhone worm, dubbed as Ikee, has been discovered spreading "in the wild" in Australia.

Affected owners of the popular iPhone mobile phone will find that their iPhone wallpaper has been altered to a picture of Rick Astley (of Rickroll fame) and the message "ikee is never going to give you up".

However, the worm is only able to infect devices that have been "jailbroken" by their owners. Jailbreaking removes iPhone's protection mechanisms, allowing users to run any software they want, according to F-Secure firm.

The worm targets users who have jailbroken their phone but have not changed their default root login password. It will search for vulnerable iPhones by scanning a handful of IP ranges ? most of which are in Australia. At the moment, F-sekure has no confirmed reports of Ikee outside of Australia.

After Ikee infects a phone, it disables the SSH service, preventing reinfection.

To protect your jailbroken iPhone, users should change their root password.

"The creator of the worm has also released full source code of the four existing variants of this worm. This means that there will quickly be more variants, and they might have nastier payload than just changing users' wallpaper or might try password cracking to gain access to devices where the default password has been changed," Mikko Hypponen of security firm F-secure.

The author of the ikee iPhone worm is Ashley Towns. He has been speaking to the media who have contacted him via his Twitter account

In an interview with ABC News, the 21-year-old student was asked if he knew how many iPhones had been affected:

"Due to the nature of it, it's kind of hard to tell, I know my phone hit about 100 alone but from there I have no idea," he said.

Towns has said on his Twitter page that he is receiving requests from people for the source code to his worm. Security firsm Sophos has contacted him requesting that he does not share it with any further people - as it could lead to more malicious iPhone malware being written in the future.

It remains to be seen whether the author of the first iPhone worm will recognise the seriousness of what he has done, and take appropriate steps to minimise the damage.