This was before cable boxes, I think (or maybe they were only needed if you had a fancy cable package). At least around here, there was a physical RF filter tha

This was before cable boxes, I think (or maybe they were only needed if you had a fancy cable package). At least around here, there was a physical RF filter that was removed at the cable box that delivered cable to your house, if you subscribed to HBO. I swear I remember hearing about people removing the filter themselves and then getting in trouble when the cable company found out. On most sets you could turn the knob to channel 2 and get a distorted picture and audio for HBO if you weren't a subscriber. I always figured that it was either leaking out from the cable, or maybe a TV or something wasn't shielded well enough. I'm out of my depth on that though, so I'd just be guessing.