That, as I recall, has been there since the Brazilian phpBB hacker worms ("Santy") hit over Christmas 2004. Google was being used to identify vulnerable phpBB forums to infect and Google took action to deny the search queries. Note the search query in that link is: Out of curiosity, why were you trying to do this search, Jorge?
I was thinking the exact same thing... the only reason people run that search query is to find phpbb boards to exploit... shady practice...
ohh i won't be able to sleep now, with all those nightmares of people thinking that way... nah... honestly, it has to do with a new project related with phpbb, i wanted to know my audience.
Well, you're going to have trouble searching with that query with the major search engines. After Google banned the query, the Brazilian jerks brought out a variant of Santy which used Yahoo, so Yahoo followed suit in banning the query. I would imagine that other search engines followed suit, though I admit I haven't tried them.