It's happened to me during an F1 stream. There used to be a fella on Reddit who'd post really high quality, reliable F1 streams and was well regarded, but over time random edits would start to creep in, to the point where it randomly flashed porn into the stream.

Sometimes I'd have it plugged into the living room TV when the kids were around but luckily in that instance nobody saw anything. I avoid using streams after that.