Apple iBooks users who jailbreak their iPhone may find themselves locked out of their own book collection.

Apple has allegedly built a jailbreak checker into iOS version 4 and above to see if someone's iPhone has been jailbroken with a hack known as greenpois0n, according to the Web site Social Apples. If the hack is found, then Apple reportedly blocks access to content in the latest version of the iBooks e-reader app.

The unlucky iBooks user who reported the experience on Social Apples ran into the following error when trying to access an e-book on a jailbroken device: "There is a problem with the configuration of your iPhone. Please restore with iTunes and reinstall iBooks."

Apple did not respond to a request for comment on the matter.

But comments to the story on Social Apples revealed similar tales from other iBooks users and opened up the whole issue of whether Apple is in its rights to "cripple" certain functionality on jailbroken phones.

Jailbreaking has always been a contentious issue between device makers such as Apple and their customers. A ruling from the U.S. Copyright Office last summer found that the mere process of jailbreaking does not violate federal copyright law, as Apple had asserted. But jailbreaking does violate the license agreement between Apple and its customers, which most jailbreakers accept as the cost of freeing up their devices.

The government ruling certainly doesn't stop Apple from cooking up ways to disable jailbroken features and unauthorized apps on its iDevices. But in the case of iBooks, some of the commenters argued that Apple is preventing them from accessing e-books that they legally purchased.

Technically, the point may be moot since already some hackers have developed a way around the iBooks issue through other hacks and promise that greenpois0n should soon be patched to fix the problem. But it still leaves open the question of how far Apple can and should go in its fight to stop jailbreaking, and what users can and should expect when they jailbreak their phones.