[Source]

Jonathan Zdziarski, author of the book iPhone Forensics Manual, has recently discovered that the new iPhone OS (2.x) has a blacklisting method. In a nutshell, the iPhone will contact home, retrieve a list of unauthorized apps, and then disable any apps installed on your phone that match the blacklist.

“This suggests that the iPhone calls home once in a while to find out what applications it should turn off. At the moment, no apps have been blacklisted, but by all appearances, this has been added to disable applications that the user has already downloaded and paid for, if Apple so chooses to shut them down.

I discovered this doing a forensic examination of an iPhone 3G. It appears to be tucked away in a configuration file deep inside CoreLocation.”

Please note that this is entirely different from Apple removing/delisting the application from the App Store. For example, even though Apple pulled NetShare recently, people who have already purchased the app can still use the NetShare to its full functionality. And while there are currently no apps listed on the blacklist, if Apple decided to add, say NetShare, to the mix, the application would no longer be functional.

The blacklist is located on the following remote URL:

https://iphone-services.apple.com/clbl/unauthorizedApps

not only that.... it might be able to detect those Cydia and Installer app in your jail broken phones..

hehe.. that's why I still maintain FW 1.1.4 in my original iPhone, as recommended by Zibri..