Sydney  - Australians were warned Thursday that a harmless worm affecting iPhones could prompt hackers to steal data.

Last week, Australian software whiz Ashley Towns released a worm that installs on the iPhone wallpaper a photograph of 1980s pop singer Rick Astley.

The 21-year-old said it was a bit of fun and to remind the small number of iPhone users that leave their devices unprotected by pass codes that they are vulnerable to hacking.

Computer experts interviewed on radio warned that a variant of the so-called Rickrolling worm could allow hackers to pilfer confidential data like contact lists and internet bookmarks.

Computerworld magazine also warned owners of Apple mobile phones who have "jailbroken" their devices so they can install unauthorized software that they have effectively torn down their own phone's security system.