A WebmasterWorld thread referencing a Google AdSense Help thread where a Googler said they have made adjustments to the AdSense invalid click filter to better block clicks from a specific third party crawler.

A couple weeks ago, Andrew from the Google AdSense team said:

Two main points here:

(1) Google is aware of a network that is generating nice amounts of invalid clicks on AdSense ads and they are going to or already have stopped it.

(2) Google will remove invalid clicks from estimated earnings reports more quickly so the difference between the estimated and actual will be smaller.

So you may have noticed earnings changed recently do to this.

Forum discussion at WebmasterWorld & Google AdSense Help.