It wouldn't be too hard to make an ad-blocker that used CSS and Javascript to do all of the blocking during page render. It'd be an inefficient use of bandwidth and rendering time, but it'd be able to block 100% of ads and undetectable from the web server.
In fact, before Opera had a built-in ad-blocker, I think there was an ad-block extension built on its "User Javascript" and custom CSS abilities.
function verifyAds() {
if (!adContentsVisible()) {
loadAdContents();
}
setTimeout(verifyAds, 1000);
}
verifyAds();window.adContentsVisible = function () { return true; }
(function() {
// local scope, can't override
})();
function adContentsVisible() { return true }Render the page, identify the regions of the resulting bitmap which are ads, and blank them out. The browser can always just lie at the end, even after running all of the JavaScript and marking all of the DOM elements to visible.