Google Adsense is one of the easiest programs for new webmasters to monetize their sites and start to see earnings immediately. However, one of the biggest problems faced by Google is of invalid clicks or click-fraud. This is done by clicking on the Ads in a publisher's website for the purpose of increasing click counts (and thereby earnings) or to increase the advertising costs of a competitor. The repercussions of click-fraud is being banned (for the publisher) and inflated costs (to the advertiser).
Here's a link to a must-read paper for anyone who makes money with the Adsense program.
