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I've never heard of this, and I think it's still pretty rare, but I suppose anything connected to the Internet can be used to try to scam you. And smart TVs are no different.
The latest scam, coming to a television near you
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The first thing I wanted to know, and the only thing they left out, was HOW? The best way to prevent being hacked is to know how they'll try to do it. So I looked it up and this explains how someone can get your SmartTV to give a bogus pop-up window, etc.
12 Ways Hackers Can Attack and Take Control of Your Smart TV