This would be so easy for the terrorists to do that I'd be surprised if they hadn't already tried it.
Translation of text uncovered in the last two weeks from an AQ website. I believe there are a couple of threads on this in FR somewhere:
"We promise that we will not let you live safely, and you'll not see from us anything else just bombs, fire, destroying homes, cutting your heads. Our mujahideen is coming to you very soon to let you see what you didn't see before."