AdWords~Pay-Per-Click advertisements (PPC)

Advertisers specify the words that should trigger their ads and the maximum amount they are willing to pay per click. When a user searches Google's search engine on www.google.com, ads for relevant words are shown as "sponsored link" on the right side of the screen, and sometimes above the main search results.

The ordering of the paid listings depends on other advertisers' bids (pay for placement P4P) and the "quality score" of all ads shown for a given search. The quality score is calculated by historical click-through rates and the relevance of an advertiser's ad text, keyword, and landing page to the search, as determined by Google. The quality score is also used by Google to set the minimum bids for an advertiser's keywords.

The auction mechanism that determines the order of the ads has been called a "generalized second price" auction. It is a variation of the Vickrey auction.

AdWords~Legal context

AdWords has generated lawsuits in the area of trademark law and click fraud. In 2006, Google settled a click fraud lawsuit for US$90 million.

Overture Services, Inc. sued Google for patent infringement in April 2002 in relation to the AdWords service. Following Yahoo!'s acquisition of Overture, the suit was settled in 2004 with Google agreeing to issue 2.7 million shares of common stock to Yahoo! in exchange for a perpetual license under the patent.

AdWords~Technology

The AdWords system was initially implemented on top of the MySQL database engine. After the system had been launched, management decided to use a commercial database (Oracle) instead. As is typical of applications simultaneously written and tuned for one database, and ported to another, the system became much slower, so eventually it was returned to MySQL.

AdWords~History

The AdWords product was launched in 2000. At first advertisers would pay a monthly amount, and Google would set up and manage their campaign. To accommodate small businesses and those who wanted to manage their own campaigns, Google soon introduced the AdWords self-service portal. As of 2005, Google provides a campaign management service called Jumpstart to assist advertisers in setting up their campaigns.

In 2005, Google launched a program to certify individuals and companies who have completed AdWords training and passed an exam. Due to the complexity of AdWords and the amount of money at stake, some advertisers hire a consultant to manage their campaigns.

What is AdWords ?

AdWords is Google's branded P4P service. It provides relevant text-based ads on Google's site, and on external sites willing to host Google ads. On the Google site, they are pure text, and thus difficult to block. However, on external sites, they are hosted within an IFRAME tag, making them easy to remove with advertisement blockers like the Mozilla extension AdBlock. Companies wishing to promote their products can enroll in this program to their adds on Google or on websites which use AdSense, the other side of the Google advertising model.

AdSense~Criticism

Due to concerns about click fraud, Google AdSense has been criticized by some Search engine optimization firms as a large source of what Google calls "invalid clicks" in which one company clicks on a rival's search engine ads to drive up its costs. Some publishers have been blocked by Google, complaining that little justification or transparency was provided.

To help prevent click fraud, publishers can choose from a number of click tracking programs. These programs will display detailed information about the visitors who click on the AdSense advertisements. Publishers can use that data to determine if they've been a victim of click fraud or not. There are a number of such commercial scripts available for purchase. An open source alternative is AdLogger.

Google has also come under fire for allowing AdWords advertisers to abuse trademarks. In 2004, Google started allowing advertisers to bid on any search terms, including the trademarks of their competitors.

The payment terms for AdSense customers have also been criticized. Google withholds payment until an account reaches US$100 , but many small content providers require a long time - years in many cases - to build up this much AdSense revenue. These pending payments are recorded on Google's balance sheet as "accrued revenue share". At the close of its 2006 fiscal year, the sum of all these small debts amounted to a little over US $370 million - cash that Google is able to invest but which effectively belongs to its customers.

AdSense ~Abuse

Some webmasters create sites tailored to lure searchers from Google and other engines onto their AdSense site to make money from clicks. These "zombie" sites often contain nothing but a large amount of interconnected, automated content (e.g.: A directory with content from the Open Directory Project, or scraper sites relying on RSS feeds for content). Possibly the most popular form of such "AdSense farms" are splogs ("spam blogs"), which are centered around known high-paying keywords. Many of these sites use content from other web sites, such as Wikipedia, to attract visitors. These and related approaches are considered to be search engine spam and can be reported to Google.

There have also been reports of Trojans engineered to produce fake Google ads that are formatted to look like legitimate ones. The Trojan Horse apparently downloads itself onto an unsuspecting computer through a web page and then replaces the original ads with its own set of malicious ads.

How AdSense works

Each time a visitor visits a page with an AdSense tag, a piece of JavaScript writes an iframe tag, whose src attribute includes the URL of the page. Google's servers use a cache of the page for the URL or the keywords in the URL itself to determine a set of high-value keywords. (Some of the details are described in the AdSense patent.) If keywords have been cached already, ads are served for those keywords based on the AdWords bidding system.

AdSense for search

A companion to the regular AdSense program, AdSense for search lets website owners place Google search boxes on their pages. When a user searches the web or the site with the search box, Google shares any ad revenue it makes from those searches with the site owner. However, only if the ads on the page are clicked, the publisher is paid. Adsense does not pay publishers for mere searches.