Android :: Blocking Intents From Launching?

On the market, there's an application called App Protector, which seems to effectively block the launching of configured activities until a password is correctly provided. By default, it blocks access to itself (not very interesting), Settings, and a few others. I wrote my own app to launch settings (rather than doing so through the home screen) and App Protector continued to do the job it claims to do.
When an activity that is protected is started, App Protector's password input activity is shown instead. Once the correct password is provided, the activity that was started comes to the front.
First -- does anyone know how this app is able to get between the rest of the system and the activities it protects? I would like to do something along these lines in my own application as well. Perhaps this app is receiving a broadcast about other activities coming to the foreground, and when the foreground activity is protected, it forces itself to the foreground?
Second -- does anyone know how well this technique will stand up to attack? Are there other ways to circumvent, where start Activity(...) fails to? It seems that one could use adb to un install it, thus removing its protection easily, but if I pursue my plans here, the app will be a part of a device's firmware (which, I assume, offers some protection against its apps being installed?)