Facebook has denied it's listening to your conversations picked up by your phone's microphone. Some have noticed a strange coincidence when discussing certain things, and some kind of ad re-marketing is occurring. I don't doubt there's re-marketing going on, but listening to the microphone would be a really bad move, imho.
Facebook's VP of Ads, Rob Goldman, "We show ads based on people's interests and other profile information - not what you're talking out loud about," it said.
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bbc.co.uk...]