So basically a weapon that can annihilate any first world country? Nice.
You pretty much hit the nail on the head with this. Terrorist cells would have the means to use WiFi, but considering where they have to operate these days, I highly doubt they would use WiFi or even be that stupid to in the first place. (Edit:If they are that stupid, so much the better for us)
I'm reminded of the movie Sneakers [http://www.imdb.com/title/tt0105435/]. Scientist comes up with a code that breaks all cyphers. What doesn't become apparent until a little later is it was only all American cyphers that this code breaks. It would only be good for using against Americans.
This feels like what we have here. The military have no sanction to use weapons within US borders(at least not without presidential authority), but how long before certain agencies decide to borrow it? Homeland Security will want it, the CIA, the FBI, the NSA...
This is a dangerous monster, and I am hoping since we even know of it that its capabilities are actually not much. Hopefully it just jams Wifi signals and nothing else.