When Apple released iOS 5.1 earlier this month, users who love to use jailbreak utilities were highly recommended to stay away from the firmware update. The iPhone Dev Team said in its blog post that with A5 devices like iPad 2 and iPhone 4S, it was not possible to downgrade to any older iOS 5.x firmware, even if the SHSH blobs (Signature HaSH blobs) are saved.

iOS 5.1 Jailbreak: Loophole Found That Allows Downgrade iOS 5.1 To iOS 5.0.1 on iPad 2, iPhone 4S

So far, only non-A5 devices like the iPhone 4, 3GS, the original iPad and the iPod touch are downgradable back to both iOS 5.0.1 (custom firmware only) and iOS 4.x provided the users of the devices have SHSH blobs and APTicket saved for the firmware they want to downgrade to.

But this is likely to become passé soon as iOS developer and hacker iH8sn0w announced Sunday via Twitter that he had found a bug in Apple's APticket system that allowed him to downgrade his iPad 2 from 5.1 to 5.0.1.

Found a loophole in Apple's apticket system. Restored my iPad 2 to 5.0.1 from 5.1. Works on all A5 devices, iH8sn0w tweeted.

According to a Redmond Pie report, the hacker also believes that the exploit he had discovered would also allow firmware downgrades on Apple's new iPad running on the new A5X processor. Obviously this will only be possible when newer firmwares become available due to the fact that all new iPads were actually shipped with iOS 5.1, which is the current version, the report added.

What the information essentially means is that the owners of iPad 2 and iPhone 4S are now welcomed to the downgrade party. Once the exploit in question is made public, they will be able to restore their devices to any firmware they want, providing that they have the appropriate SHSH blobs saved.

Apart from the tweet from iH8sn0w, there're no word about an official release of the APTicket system loophole yet. To know how to downgrade iOS 5.1 to 5.0.1, 5.0, 4.3.3 and 4.3.5 on non-A5 devices, click here.

Meanwhile, according to the latest figures released by iOS app developer David Smith, iOS 5.1 has hit roughly 61 percent adoption among owners of iPhones, iPads and iPod touches within just two weeks.

Credit: David Smith

Smith has been tracking the versions of iOS with the help of his Audiobooks app. Audiobooks is universal so provides data for both iPhone and iPad. The free and paid versions of Audiobooks together get around 100k weekly downloads so provides a statistically meaningful data set, Smith said.

He also speculated that the new over-the-air update system may cause an increase in update over previous releases which required devices to be plugged into iTunes for updates, Redmond Pie reported.

According to a report by TNW, iOS 5.x hit 75 percent adoption earlier in March, while Android 4.0 Ice Cream Sandwich was stuck near 1 percent only. Now, the latest version of Apple's iOS software is already running on a majority of Apple's devices, while ICS still languishes at 1.6%, the report added.

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