Google announced a new change to ad serving with in Google AdSense. Now, if Google finds a better performing ad type, even if it is smaller than the ad slot you currently set up, Google will place the ad in that ad slot and place white space around it.

This is called, “Similar Sized Display Ads” where Google will try to throw in better performing ads even if they don’t look as good.

It may look like this, with white space around the ad box:

Google explained on the opt out page, under Allow & Block Ads > Ad Serving:

Here is a screen shot on how to turn this off:

Seems like most AdSense publishers are happy with this new change.

Forum discussion at WebmasterWorld.