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Steve Wozniak has a warning for anyone who uses social media ... the platforms are eavesdropping on your private conversations, and sending that precious data to advertisers.

We got Steve at Reagan National Airport in D.C. Friday and just had to ask him if he's worried about Facebook, Instagram and others infringing on his privacy ... the Woz says he's terrified, and you should be too!!!

Steve knows what he's talking about ... the dude co-founded Apple, and he's very much plugged into Silicon Valley and all aspects of tech.

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The paranoia surrounding social media spying is top of mind right now after Gayle King called BS on Instagram chief Adam Mosseri's assertion the platform does NOT listen in on your private convos.

Woz says he ain't buying the company line, either ... and he explains why anything you say in the presence of your electronics is readily made available to all sorts of entities.