The wikipedia article on Limewire says that "LimeWire 5.5.11 and newer have been disabled using a backdoor installed by the company".

How are such backdoors implemented? Is it as simple as the the program going out and checking a web service and disabling itself? If it's in fact so simple, it has to be stored somewhere on the user's drive (in a plist, or in the registry for example). It's hard to imagine no one has in fact figured out a way to turn that flag off and use the program.