Some publishers have truly clicked on their own AdSense ads by accidents. Some visitors have also clicked on AdSense ads on the sites of these publishers by accident.
In the past your visitors could click on both the background and full text of an ad. With the change made by Google they now can click only on the title and URL of a text ad.
This could reduce the earnings of some AdSense publishers while helping advertisers so that they would only be paying for clicks that were meant to be made. However Google says it could also help publishers because it would encouraging additional spending by AdWords advertisers.
Here are two Google links that explain this for the AdSense publisher and the AdWords advertiser.
Inside AdSense: Accidental clicks fade into the background
Inside AdWords: A change to text ads on the content network
In the past your visitors could click on both the background and full text of an ad. With the change made by Google they now can click only on the title and URL of a text ad.
This could reduce the earnings of some AdSense publishers while helping advertisers so that they would only be paying for clicks that were meant to be made. However Google says it could also help publishers because it would encouraging additional spending by AdWords advertisers.
Here are two Google links that explain this for the AdSense publisher and the AdWords advertiser.
Inside AdSense: Accidental clicks fade into the background
Inside AdWords: A change to text ads on the content network