An iPhone worm has started jumping between jailbroken devices, taking advantage of users who have replaced the phone's software but failed to create a new root password, security firm F-Secure stated on Monday.

The worm, dubbed "Ikee," replaces the phone's wallpaper with a picture of Rick Astley, the singer whose song "Never Gonna Give You Up" has become infamous as the punchline in the Internet prank known as "rickrolling." Once on a phone, the program scans a limited number of IP addresses belonging to networks mainly in Australia, according to F-Secure.

"The creator of the worm has released full source code of the four existing variants of this worm," Mikko Hyppönen, chief research officer for F-Secure, stated in a blog post. "This means that there will quickly be more variants, and they might have nastier payload than just changing your wallpaper or might try password cracking to gain access to devices where the default password has been changed."

Since the iPhone's debut in 2007, security researchers have focused on hacking the popular device. Last summer, consultant Charlie Miller and student Collin Mulliner discovered a way to exploit the phone using the common short message service (SMS). The bug was short-lived; Apple fixed the issue a month after it was announced.

The Ikee worm does not affect iPhones that have not had their operating systems' overwritten, a process known as jailbreaking that allows users to install non-Apple-approved software and programs.

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