Apologies for possibly being pedantic, but I do think this is necessary to point out. A lot of people seem to think that "passive" refers to statements that are vague about agency, or often something else vaguely along those lines. But active-vs-passive has nothing to do with that!
Now one could say, well, that's just not how people are using the word "passive" these days; but the thing is, I don't think whatever notion people are trying to express via "passive" is a useful one. Sometimes it means "vague about who's responsible", but often it doesn't; I don't think there's a useful notion worth salvaging in there.
Anyway for way more on this you can see Geoff Pullum's article on it[1], or the whole "passives" category[2] on Language Log...