Botnet takeover

Recently my computer got taken over by a botnet and started generating spam. It generated so many that a watchdog service shut down my IP address. I had to jump through hoops to get my IP back and prove it was me.

The question is WHY did Norton Internet Security detect this and stop it?

Is there an internet security out there that will do more than Norton?

I downloaded and am running RUBotted alongside Norton Internet Security as some postings say it detects Botnet take overs.