Norton AntiVirus is a component of NIS. It has a worm blocking feature, kind of like a small firewall.
Norton Internet Security includes Norton AntiVirus. NIS includes outbreak alerts, the worm blocking feature is replaced by NPF which has an integrated Intrusion Protection feature. NIS, though works with signatures, also works with heuristics.
The 2007 version of NIS includes improved rootkit detection, improved virus protection, improved anti-spyware protection, advanced firewall support, intrusion protection, simpler design, optional parental controls, and is designed to not hog your system resources as much as previous Norton products.
If you are going to update to a Symantec product, i recommend Norton 360. Contrary to most people's beliefs, Norton 360 gives you better protection than McAfee, AVG, Avast and other applications. It has been ranked as one of the highest security applications and has recently won the CNETs Editors Choice Award. Norton 360 gives you:
-improved antivirus
-improved rootkit detection
-improved anti-spyware
-improved advanced firewall with intrusion protection
-online transaction security
-initial 2 GB of online storage
-automatic backup and restore
-pc tuneups
-website authentication
-anti phishing
-IM security
-email security
-optional free antispam
-optional free parental controls