The other day I was watching the SCIFI channel when I lost the picture and sound. Almost immediately, QVC (a shopping channel) came on with tornado warnings for nearby counties scrawling across the top of the screen. While the storm information was scrolling, I wasn't able to change the channel.
BTW -- I've got Comcast. The set I was watching is hooked to a box which allows more access than just plugging the cable wire into the set.
BTW 2 -- The QVC sales woman was so *&^%$ perky and annoying that I vowed never to voluntarily watch that channel.