Comment by talent_deprived

For disabling X11 middle click paste, I found an interesting SO post but the best answer I saw and tested myself and it works, was the one by Suraj Inamdar about one third of the way down the page:

https://unix.stackexchange.com/questions/24330/how-can-i-tur...

What sucks is I use middle click paste all the time so now I'll have to decide if I want to leave it disabled for potentially improving security.