AdSense Explained

AdSense is a contextual advertising program from Google. AdSense allows sebsite owners to generate income from displaying relevant advertisements on their websites. Currently, AdSense uses JavaScript code to incorporate the advertisements into a participating site.
 
AdSense Bot - Mediapartners-Google/2.1
 
The Google AdSense advertisements are relevant because Google sends out a bot, called Mediapartners-Google/2.1, to crawl websites. The bot analyzes the text on any given page and delivers ads that are appropriate and relevant, increasing the usefulness of the page and the likelihood that those viewing it will actually click on the advertising presented there. That means  the bot reports the website content to Google and AdSense. After a matching of the content of a website with ads within the Google AdWords program, AdSense can deliver relevant advertisements on the website. If it is included on a site which has not yet been crawled by the Mediabot, it will temporarily display advertisements for charitable causes known as public service announcements (PSAs).
 
The "non-intrusive" and highly relevant AdSense advertisements generate revenue on a Pay Per Click (PPC) or Pay Per Lead (PPL) basis.
 
AdSense Technology & History
 
The underlying technology behind AdSense was derived originally from WordNet and Simpli, a company started by the founder of Wordnet George A. Miller and a number of professors and graduate students from Brown University, including James A. Anderson, Jeff Stibel and Steve Reiss.
 
A variation of this technology utilizing Wordnet was developed by Oingo, a small search engine company based in Santa Monica, which was founded in 1998. Oingo focused on semantic searches rather than brute force string searches. Oingo changed its name to Applied Semantics, which was then bought by Google for $102 million in April 2003, to replace a similar system being developed in house.
 
Abuse Of AdSense
 
Some webmasters create sites tailored to lure searchers from Google and other engines onto their AdSense site to make money from clicks. These 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.
 

MFA (Made For Adsense) is a site or page with little or no content, but filled with advertisements so users have no choice but to click on ads. Such pages were tolerated in the past, but due to complaints Google now disables such accounts.
 

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.
 
You can find Google AdSense at https://www.google.com/adsense/ and the official AdSense Blog at http://adsense.blogspot.com/ for further information.