Just under a month ago, Google released a really large ad format – 300×600. The new ad format, as Google said, is “brand friendly” and is also typically called a half page unit.

What started happening was that publishers started putting up to three of these ad units on their pages, leaving virtually no room for content.

So Google announced a change in policy to just allow one of the 300×600 ad units on a page at a time. You can have up to three ad units on a page, but only one 300×600 unit is allowed on the page.

If you added multiple, you have until January 10, 2013 to remove it.

Google wrote:

Forum discussion at WebmasterWorld.