For desktop and laptop computers, see Norton Security Suite on http://constantguard.xfinity.com/products-and-services/norton-security-suite/ under FAQ:
Can I download Norton Security Suite on more than one device?
Yes. Norton Security Suite can be downloaded on up to seven devices for residential customers.
For mobile devices (phones and tablets) they offer "Norton Mobile Security" for $20/yr. See http://constantguard.comcast.net/products-and-services/. The App and Play stores have many security apps available, some of which are free.