I bought the download version, and had to download N360 onto all 4 systems. (I bought a 5-license one.) Then I installed it onto each one, grabbed (copy/paste) the CD key/registration off my account on the web, and everything worked as expected.
Visitor informs this:
Just one small suggestion: Download could be performed one time on one machine, copied to a flash drive, and this copied file could be brought to the other three machines to perform the installation. This would save on time waiting for downloads.
Please follow the instructions in this document to install Norton 360 on an additional computer: