Legally, you have to tell other users that it is installed.
Oh, goodness, absolutely. I know that, in the unlikely event that
I were to install spyware on
MY family's computers, I would certainly be sure to advise all users of its existence. Yeppers. I sure would. Because I wouldn't want them to do something on there that they wouldn't want me to see, nosireebob.
Of course, I'd have to make a mental note to mention that to everyone...I'm so forgetful that way...dang, I can't even remember if I put keyloggers on our computers...