I think it is worth mentioning that in São Paulo people tend to use the word "grafite" for artful murals and drawings and "pixação" for the stuff that is seen as vandalism. (there are some grey areas but that is the jist of it)
As an aside, I remember a short Brazilian documentary on São Paulo's "reverse graffiti" (doing a drawing or mural by skillfully removing dirt from a dirty wall, so that the white spaces create an image) where the police detained the artist doing it, despite the fact he was literally cleaning the wall.