This question already has an answer here:
I stay logged into Google. I would very much like to permanently blacklist sites that I know to be SPAMmy or low quality from showing up in some of the modules like news and search. Any suggestions on how? I know how to do it case by case in search (-site:lame.example.com) but that's not permanent.
EDIT: The solution presented below does in fact work for search (thanks!) but not for news - anyone?