Hi greglica, are you installing your Norton please follow this link https://www.xfinity.com/support/articles/norton-security-download-install-pc. From that page it looks like it should only ask for a Xfinity Username and Password.
The link supplied in the above post does not work (the period is included in the link). The corrected link ComcastPhill is suggesting is:
Additional helpful info may be located in the following Knowledge Based Article from Norton:
Helpful info may be located in the following Knowledge Based Article from Norton: