First of all, open the TV and disconnect the wireless radio from the main board, on mine (Samsung) it was just unplugging one cable (AI or Google it). I dislike doing stuff like that, but it was easy in my case, maybe you'll be lucky, too.
Second, never use the "apps" built into the TV.
Next, don't plug Ethernet into the TV. Plug HDMI cables into the TV.
Use a box of your choice on the other end of the HDMI cables. This is now the box that you trust. (Roku? Shield? Blu-ray? MacBook? PC? Linux? Playstation? XBox? Whatever you want.)
The Smart TV itself is now fine. Choose the devices you plug into it to play content. The TV just shows it.
Second, never use the "apps" built into the TV.
Next, don't plug Ethernet into the TV. Plug HDMI cables into the TV.
Use a box of your choice on the other end of the HDMI cables. This is now the box that you trust. (Roku? Shield? Blu-ray? MacBook? PC? Linux? Playstation? XBox? Whatever you want.)
The Smart TV itself is now fine. Choose the devices you plug into it to play content. The TV just shows it.