Yes, even if you have powered off your phone, you are not safe. The only way to be sure is to take your battery out of your phone.. so good luck with that Iphone users!
http://feedproxy.google.com/~r/gizmodo/full/~3/dIm-SZ9eDvs/the-fbi-can-remotely-activate-microphones-from-android-996086550
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