iTunes is only available for a few select platforms...
The scheme Apple outlined in the patent application would rely on a cryptographic key generated prior to the hardware reaching the user. As an application launches, the technology would inject code into the app's executing code stream, generate data that's sent to a digital rights management module, then compare that signed data with the key. If they match, the application continues to open. If not, it's stopped in its tracks.
Such checks could be done on a very frequent basis, said Apple's patent application.
APL hackers do it in the quad.