[Quote:]

Advertisers have been able to direct online messages based on demographics, income and even location, but one element has been largely missing until recently: immediacy. Advertisers booked slots in advance, and could not make on-the-fly decisions about what ads to show based on what people were doing on the Web.

Now, companies like Google, Yahoo and Microsoft let advertisers buy ads in the milliseconds between the time someone enters a site’s Web address and the moment the page appears. The technology, called real-time bidding, allows advertisers to examine site visitors one by one and bid to serve them ads almost instantly.

For example, say a man just searched for golf clubs on eBay (which has been testing a system from a company called AppNexus for more than a year). EBay can essentially follow that person’s activities in real time, deciding when and where to show him near-personalized ads for golf clubs throughout the Web.

Advertisers can go ahead and buy anything they want in the milliseconds between me entering an address and the page appearing. As long as the actual appearance of the page is under my control (and on my computer it will be), Adblock will have the last word.