I guess it could be done using some combination of first placing into every HTTP header: "Refresh: 2;URL=htpp://www.grisoft.com/", which would then allow a piece of Javascript on the web page up to 2 seconds to figure out if the visitor is a real browser (maybe even including some DOM checks too), and then acting accordingly (ie: sending the user to a page without the redirect header). If AVG's http fetcher doesn't execute the Javascript or fails to pass the browser test, then it gets redirected back to AVG's site because of the HTTP header.
Convoluted? Yes. Will it work? It should, unless AVG decides to implement a full Javascript engine and DOM stack in their http fetcher. Also, the initial re-direct doesn't have to go to Grisoft, it could go each time to a randomly selected site from a list of their competitors <evil grin>.
I think AVG is really playing with fire, it's really only a matter of time before things like this start popping up as defense mechanisms.
I think the solution should be fairly simple. Since AVG is not a real browser, despite telling a web server that it is, it should be easy to craft a piece of Javascript and cookie on a webpage that would return a proper result in a real browser like IE, Firefox, Safari, or Opera. If a proper result is not returned, then the web server can just do a 302 meta redirect to AVG's website as mentioned earlier. If implemented widely on web servers (say as an apache module or PHP patch) this, in effect, would cause AVG to become it's very own DDoS attacker. I don't think they would want this, but it'll probably happen if they don't re-think the way they do things.
Convoluted? Yes. Will it work? It should, unless AVG decides to implement a full Javascript engine and DOM stack in their http fetcher. Also, the initial re-direct doesn't have to go to Grisoft, it could go each time to a randomly selected site from a list of their competitors <evil grin>.
I think AVG is really playing with fire, it's really only a matter of time before things like this start popping up as defense mechanisms.