Are all the types of satellites that orbit today public knowledge?

I read somewhere that since the 60's a lot of space junk piled up up there, and that org.s like nasa keep track of them, in case they misbehave. I'm guessing among these junk there were active warheads, too, cause of the cold war era etc. I know a lot of satellites are used for military purposes to this day but I want to know what else is up there? How advanced are they? We don't see them with our eyes, but we know they are there. However do we also know what they can do?