Web Shield - How does it Work?

Hi. Been using Avast! for awhile now and am satisfied with it. One of the features that I really like is the WebShield module which blocks malicious web sites. It saved me more quite a number of times. I like how the Avast! icon spins while a web site is loading. It tells me that it’s actually scanning the page before it downloads the content (correct me if I’m wrong). I don’t mind the additional overhead.

Just curious as to how it detects if a site has malicious content or not?
I’ve read of a program called ‘Spywareblaster’ which also prevents malicious sites from infecting a computer. Does Avast! work the same way?

Anyway, great job and keep it up!

SpywareBlaster works with immunization, preventing the access.
avast WebShield scans the http traffic and block the connection to infected sites.
avast NetShield block access to infected sites also.