Anti virus is just anti virus, internet security is Firewall and antivirus. That's the jist of it. I'm currently using Internet Security and Kaspersky detects every single thing. It's so great that it prevents photoshop and Quicktime (online trailer watching) from launching.
Basically it scans everything that is downloaded to your computer while surfing the web. opening web pages etc etc. EVERYTHING!!!
On a side note, you can install kaspersky software on three computers. Speaking of it, I think I need to get another copy of it as my key is about to expire.