That's exactly how Google does it. Please see http://www.chromium.org/developers/design-documents/safebrowsing http://www.chromium.org/developers/design-documen

That's exactly how Google does it. Please see http://www.chromium.org/developers/design-documents/safebrowsing http://www.chromium.org/developers/design-documents/safebrow... . Periodically, Chrome will download a list of hashed URLs believed to be dangerous. As you surf the web, Chrome checks client-side if the URL matches anything in the hashed list. Only if the hash matches will Chrome initiate a more in-depth check.