The title of the post says it all doesn’t it? Apple against all the odds has made an anti-jailbreak kid out of its latest version of iBooks, iBooks 1.2.1 as the book reading app has been observed to slose itself when it detects itself running on a jailbroken iDevice.
Here’s how iBooks goes about its anti-jailbreak task:
iBooks tries to run a small program that has deliberately not been correctly signed to work on the iOS device. Normal devices will refuse to run this; iBooks detects that failure and loads as usual. However, jailbroken devices will (by default) run the program fine, which iBooks also detects and refuses to go any further.