This information gets sent automatically to every ad company with a presence on a Web page unless the website owner takes steps to prevent it.

WSJ: They Know What You're Shopping For

This means that advertisers could do things like automatically create scores of ad campaigns and test different ads on LinkedIn, or quickly change spending across LinkedIn and other social media outlets in real-time, LinkedIn says.

FORBES: LinkedIn Targets Ad Growth With New Ads API

This page's creator is also an amateur horror film producer, and it shows in the site's layout, including clever artwork and mood music that automatically downloads and plays ad nauseum as long as you are on a page.

CNN: Halloween spirits are on The Web

With the right analytics built in, an ad can get automatically tweaked to improve response, or maybe a new app is created because someone raved on Twitter.

FORBES: Technology

The idea is to automatically pause gameplay for an unavoidable ad to come up for a certain product.

FORBES: Sony Files Patent that Would Pause Games to Show Ads

Suppliers can automatically accept offers or control the acceleration of payment on an ad-hoc basis according to their needs.

FORBES: Written by By Drew Hofler

But it appears that one savvy advertiser is using it in a promoted tweet (a recently introduced Twitter ad product where an advertiser can purchase the tweet that automatically appears at the top of a given search).

FORBES: Connect

So Schoemaker says he sets his web pages to automatically display legitimate content to the Google spider, while giving other users the ad-filled arbitrage page.

FORBES: Bitten By The Google Spider