It depends on the site. A non-malevolent site that has malware injected into its HTML will still be caught. The content won't get a chance to see the identifica

It depends on the site. A non-malevolent site that has malware injected into its HTML will still be caught. The content won't get a chance to see the identification. A malevolent site can just track their mechanism and work around it, like not showing malware to IE6 users unless they ask for the content a second time in quick succession. (Might not work, I don't know if the AVG copy gets cached. One would hope it doesn't for the sake of sites that do browser sniffing.)