Norton Internet Security

I use norton internet security on windows xp. Every 5 seconds i get a security alert saying a remote system is attempting to access my comp. I have been told that it is people port scanning my computer. my question is why doesnt norton just block the attempts without annoying me with security alerts?

 

You have to set your security higher to block even when you "always block" the alert. Ive had this on my system as well.