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The software hole involved in a popular method for jailbreaking Apple's iOS devices has reportedly been patched by the company as part of iOS 5, the free system software update that's due out later this year.

Digging through the beta version of iOS 5, which Apple made available to developers earlier this month, the iPhone Dev-Team--a group of hackers that targets Apple devices and is not to be confused with Apple's group that designs the iOS software--has discovered a change that threatens to close a loophole the group has long exploited.

"Those of you who have been jailbreaking for a while have probably heard us periodically warn you to 'save your blobs' for each firmware.... Saving your blobs for a given firmware on your specific device allows you to restore *that* device to *that* firmware even after Apple has stopped signing it," the group wrote on its blog yesterday. "That's all about to change."

The group says Apple has implemented a system that checks for a uniquely generated chunk of data each time the phone is restored. The problem there is that only Apple has the keys to unlock that code to let the phone boot up successfully. The end result is that jailbreaking methods that took advantage of that vulnerability could be endangered if that same system is employed in the final version of the software.

The iPhone-Dev Team notes that "there may still be ways to combat this" but that it's not showing its cards just yet, since it might give Apple time to make a fix ahead of a general release. "They've stepped up their game!" the group said of Apple's security efforts.

Apple's iPhone and other iOS devices continue to be hot targets for hackers. Ahead of the release of the App Store, one of the most popular reasons to jailbreak an iOS device was to be able to install third-party software. Even after the launch of the App Store, places like third-party app repository Cydia became destinations for developers who couldn't get their applications through Apple's approval process. Another popular reason was to unlock the iPhone so that it would work on other carriers, an option Apple now offers to U.S. buyers at a hefty price premium.

iOS 5 is due out this fall. Last week Apple released a second beta of the software to developers so they could use it to test their applications for compatibility with the OS and its new features. The first beta of the software was allegedly jailbroken by a member of the iPhone-Dev Team in less than 24 hours.