This has to be the lamest piece of junk software I've ever come across. Like most retarded personal firewall software it alerts you about every damn thing under the sun. I installed it in a VMware sandbox to debug some web issues at work and within 3 minutes of installation its warning me about "lsass.exe" attempting to access something or rather.
I'm a nerd and I have NFI what lsass.exe is. What on earth makes Symantec think Joe Average is gonna know what the hell it is, and whether s/he should block it? But I digress.
The really, truly stupid part of Norton Internet Security is its Ad Blocker feature. This piece of junk attempts to strip advertising by looking for a bunch of known strings, for example if it sees "/ad" or "/adv" in a <script> src its goooorn. But it often does an incomplete job, leaving much broken HTML within the page and in combination with some IE stupidity it stops the page from loading entirely. On top of that it installs its own junk script (link refers to NIS 2003, but 2005 has the same dumbarse behaviour).
Before we knew what was causing our problems we asked one of users to try turning NIS off and he responded along the lines of "omg my intarweb is 100x faster, I always wondered why my cable was so slow, thank you so much!".
So if you were intending to buy this piece of junk please save your moola or donate it instead.