Can people tell if I am viewing their Facebook profile?

[.:Jadian:.]

For a while I would view the "public" Facebook profiles of several people I was not friends with, not because I was being a stalker or anything, but because they looked like fun people and their posts were always really funny and upbeat. As of yesterday, the four of them have changed their profiles to "private"; not only that, but they have also made their friends lists private as well. Is it because they could tell that I was visiting their profiles? I'm really worried about this. I don't want them to think I'm a creeper!