You've got to be kidding me. This is quite straight forward.

1. America has figured out how to listen to Merkel's phone calls.

2. Merkel finds out we listen to her phone calls.

3. Merkel stop using her phone for communications.

4. US is no longer able to listen to Merkel's phone calls.

Or:

1. US listens in on embassy.

2. Embassy finds out US is listening.

3. Embassy searches for and finds the bug.

4. US is no longer listening to the embassy.

Now apply this, at large, at the same time, to everyone that Snowden revealed we were spying on.