F-Secure said it has discovered the first iPhone worm, called Ikee.

The security company said that currently the only known infections have surfaced in Australia and affect devices that have been 'jailbroken' by their owners, but who have left the default root login password unchanged. However, it warned people to protect their phones.

Jailbreaking is the jargon for people who have removed iPhone's protection mechanisms, allowing users to run any software they want.

Affected users 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".

F-Secure said the worm will search for vulnerable iPhones by scanning a handful of IP ranges — most of which are in Australia. At the moment, F-Secure has no confirmed reports of Ikee outside of Australia.

After Ikee infects a phone, it disables the secure shell (SSH) service, an encyrpted mechanism that gives users access to systems supporting remote connections.

F-Secure advises that in order to protect a jailbroken iPhone, people should change their root password and has outlined steps to do this on its web blog.