Unless you have a multiple user license and haven't used them all yet... you simply don't. Otherwise its one license one machine install. And yes... they have ways of knowing.

Thank you for your time although I have a package that allows me to install it on 3 computers. I emailed the confurmation order to the other computer and tried opening and pressing the download button but it does nothing.is this not correct way thanks

I have got a new laptop as my old one is not working how do I transfer my Norton 360 over to my new laptop as I have only uesd my 3 as I my family have the other 2??