It seems that Apple has removed the jailbreak detection API from iOS, that is used to detect whether or not a device has been jailbroken. It was first added to Apple’s mobile OS when version 4.0 was released.
When the latest version of iOS was released, iOS 4.2.1, the API has either now been removed for it has been disabled, it is unclear as yet why this has been done.
What the jailbreak detection API did was let applications query the device to see if it was jailbroken, and if businesses were using the device and the API, they would be able to detect jailbroken devices and block it from accessing services like exchange.
Network World via Gadget Venue