It may be stupid to say so, but I really wanna make out that is spy software a kind of virus?
Who will tell me about them?
IMO, spyware is a kind of virus, but spy software is just a program to monitor others. A lot of people use spy software to monitor employees or their kids. These followings are some examples: remote spy software, mac spy software, mobile spy software.
I can not tell clearly, but this is the article where my idea comes from: http://www.spytech-web.com/what-is-spy-software.shtml
Hope this will give you a hint.
Off topic: What was that April Fools virus that got everyone worked up last year, I forgot the name.