Most companies don&#x27;t serve their own ads. They sell an iframe reference in a particular kind of page to someone else who runs their own adserver software, so there&#x27;s a detectable footprint for organisational reasons.<p>Quite often there&#x27;s more than one level of resale; I&#x27;ve seen five and a friend who works in the business told me he&#x27;s seen even more.<p>(Digression: I have also heard that Ghostery (.com) makes most of its money by telling companies what ads are on their web pages.)