ASK ME !! ASK ME !!
Before you continue, I want to make this clear. ad-ware is ad-ware, ad-aware is ad-aware, they are both different thing. Ad-ware is something installed on your system without your knowledge, they usually will hijacked your homepage, add a tool-bar on your Internet Explorer, pop up a windows out of a sudden and log wat website u visited.
Firewall like zone alarm, Anti-Virus like norton, even those with web filtering, will NOT block ad-ware(aka spyware). They can block banner, cookies and etc..only but that's not enuff.
Ad-ware(spyware) will also installed on your system if you download screensaver, shareware or utility, it will also be downloaded if you visit porn site, warez site . Usually they are not detectable by anti-virus and firewall, coz the program itself does not contain virus!
So, you need a dedicated ad-ware scanner. Spybot, Ad-Aware are example.
Why they can block ad-ware but firewall or anti-virus can't? Coz ad-aware prog can monitor your registry and file structure. They can detect any changes done to your file or registry when you start your machine. This is where ad-ware get "alive", they usually start to edit your registry everytime u start your machine. virus-Scanner or firewall, don't stop program from editing the registry or file. It isn't consider a virus.