Apple had introduced jailbreak detecting API with iOS 4.0 but decided to drop it with iOS 4.2.1 update. Apple’s move was too good to be true. Social Apple’s Editor Josh pointed out that the API mysteriously got activated or something after jailbreaking the iPhone with Chronic Dev Team’s Greenpois0n tool. That was discovered when iBooks 1.2.1 App was trying to open an eBook on the jailbroken iPhone device. The iPhone Dev Team member comex tweeted that “It seems that before opening a DRMed book, iBooks drops an improperly signed binary, tries to execute it, and if it works concludes that the device is jailbroken and refuses to open the book.”
Looks Apple has incorporated the App signing feature with the native Apple Apps starting with iBooks. So even if jailbreaking your device is legal, Apple won’t let you download and read DRM’d content on your iOS device. In a way it is fair on Apple’s part for you can jailbreak if you want but you would be devoid of DRM carrying content. Also it’s frustrating enough that hackers will find a work around that may condone piracy, whether the hackers want it or not. This was the first report of jailbreak detection in iOS even though the API removal was publicised.
At this stage, it’s uncertain whether this jailbreak check has been implemented just for iBooks or exists in other premium Apps that offer in-App purchases.