ndrv_setspec() integeroverflow & Jailbreaking iOS 5?

I've heard that Apple has killed ndrv_setspec() integeroverflow in IOS 5 beta which makes the phone more difficult to jailbreak. I've also heard that the IOS 5 beta was jailbroken within just 24 hours of its preview.

Can someone tell us what's ndrv_setspec() integeroverflow and what's its significance in iOS jailbreak 😒?