White List Proxy ?

After considering possible defenses to the multitude of web attacks that 
continue to surface, I keep coming to the conclusion that white lists are the 
way to go. Unfortunately as we all know, white lists are difficult to maintain 
and often overly restrictive.
 
What I imagined is a type of white list proxy which examines website content 
before feeding it to the user, it determines if there is any malicious code in 
the page, if there is it will deny the page to the user, if not it will provide 
it to the user and add the site to the white list for 24 hours. 
 
This technique would be similar to how antivirus works in scanning files before 
allowing open/run actions. 
 
Does anyone know of software that currently does this or something similar? 
Thoughts ?
 
Eric McCarty

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