Apple has reportedly added additional security protections to its iPhone 3GS handsets designed to prevent user modifications.
The new protections are said to be aimed at slowing the practice of 'jailbreaking,' or unlocking the handset to allow the installation of software not offered on Apple's App Store service.
According to reports from the iPhoneDevTeam research group, the latest versions of the iPhone 3GS handset are shipping with an updated 'bootrom' component which prevents users from removing software protections on the device.
Older 3GS handsets and previous models are still susceptible to the procedure, which can be performed by connecting the handset to a PC and running a specialised software tool.
The move is the latest in an ongoing game of cat and mouse between Apple and hobbyist developers that began shortly after the release of the first iPhone model in 2007.
The 'jailbreaking' procedure was initially developed to allow users to install additional software in the days before the App Store was launched.
While the company has never taken direct action to shut down the iPhone Dev Team developers, iPhone updates frequently erase jailbreaking software and in some cases have damaged jailbroken handsets.
